feat(editor): align selection popup and all editor control elements styling with Reader (#81)

## Summary of Changes
This pull request aligns all major interactive editor control elements in the Milkdown Crepe editor with the premium `SelectionAiPanel` / `IntelligenceToolbar` glassmorphism design.

### Changes:
1. **Selection Bubble Menu Unification:** Relocated the selection menu overrides from `Creator.razor.css` to `app.css` to resolve scoping bugs. Themed to match the Reader's selection popup 1:1.
2. **Editor Controls Theming:** Themed table cell drag handles, table actions popups, line insertion handles & add buttons, Notion-style paragraph drag handles, and slash commands menus with glassmorphic backgrounds, perimeter borders, hover transitions, and active accent states.
3. **Visibility Lifecycle Fixes:** Excluded `.cell-handle` and `.milkdown-block-handle` from explicit `display: none !important` rules when hidden, preserving their dimensions for correct JS positioning calculations and preventing handles from jumping/sliding.
4. **Table Margin Clipping Fix:** Set `overflow: visible !important` on `.tableWrapper` to allow table controls to draw cleanly into the editor canvas's padding zone without boundary clipping.

Resolves #82.

---------

Co-authored-by: Marek Jasiński <jasins.marek@gmail.com>
Reviewed-on: #81
Co-authored-by: Antigravity <antigravity@google.com>
Co-committed-by: Antigravity <antigravity@google.com>

Directory.Packages.props

@@ -4,6 +4,7 @@
   </PropertyGroup>
   <ItemGroup>
     <PackageVersion Include="FluentResults" Version="4.0.0" />
+    <PackageVersion Include="HtmlSanitizer" Version="9.0.892" />
     <PackageVersion Include="Mapster" Version="10.0.7" />
     <PackageVersion Include="Mapster.DependencyInjection" Version="10.0.7" />
     <PackageVersion Include="MediatR" Version="12.1.1" />

src/NexusReader.Application/Abstractions/Services/ISanitizerService.cs

@@ -0,0 +1,13 @@
+namespace NexusReader.Application.Abstractions.Services;
+
+/// <summary>
+/// Service for sanitizing raw input text (e.g. Markdown/HTML) to protect against XSS injection.
+/// Intended to have a Singleton lifetime.
+/// </summary>
+public interface ISanitizerService
+{
+    /// <summary>
+    /// Sanitizes the input string and returns a clean, safe version.
+    /// </summary>
+    string Sanitize(string input);
+}

src/NexusReader.Application/Abstractions/Services/IStorageService.cs

@@ -0,0 +1,18 @@
+namespace NexusReader.Application.Abstractions.Services;
+
+/// <summary>
+/// General file storage service interface for handling media uploads.
+/// Intended to have a Scoped lifetime.
+/// </summary>
+public interface IStorageService
+{
+    /// <summary>
+    /// Uploads a file stream and returns its public URL/path.
+    /// </summary>
+    Task<string> UploadFileAsync(Stream fileStream, string fileName, string contentType);
+
+    /// <summary>
+    /// Uploads file bytes and returns its public URL/path.
+    /// </summary>
+    Task<string> UploadFileAsync(byte[] fileBytes, string fileName, string contentType);
+}

src/NexusReader.Application/Common/AppJsonContext.cs

@@ -18,6 +18,9 @@ namespace NexusReader.Application.Common;
 [JsonSerializable(typeof(List<NexusReader.Application.Queries.Recommendations.RecommendationDto>))]
 [JsonSerializable(typeof(NexusReader.Application.DTOs.User.UpdateThemeRequest))]
 [JsonSerializable(typeof(NexusReader.Domain.Enums.ThemeMode))]
+[JsonSerializable(typeof(NexusReader.Application.DTOs.Media.ValidateChapterRequest))]
+[JsonSerializable(typeof(NexusReader.Application.DTOs.Media.ValidateChapterResponse))]
+[JsonSerializable(typeof(NexusReader.Application.DTOs.Media.UploadResultDto))]
 public partial class AppJsonContext : JsonSerializerContext
 {
 }

src/NexusReader.Application/DTOs/Media/MediaDtos.cs

@@ -0,0 +1,18 @@
+namespace NexusReader.Application.DTOs.Media;
+
+// Note: These DTOs are registered in AppJsonContext.cs for JSON source generation.
+
+/// <summary>
+/// Request DTO for chapter validation/sanitization.
+/// </summary>
+public record ValidateChapterRequest(string Content);
+
+/// <summary>
+/// Response DTO containing sanitized chapter content.
+/// </summary>
+public record ValidateChapterResponse(string SanitizedContent);
+
+/// <summary>
+/// Response DTO containing the uploaded media file URL.
+/// </summary>
+public record UploadResultDto(string Url);

src/NexusReader.Infrastructure/Configuration/HtmlSanitizerSettings.cs

@@ -0,0 +1,35 @@
+using System.Collections.Generic;
+
+namespace NexusReader.Infrastructure.Configuration;
+
+/// <summary>
+/// Settings for configuring allowed tags, attributes, CSS properties, and schemes in HtmlSanitizerService.
+/// </summary>
+public class HtmlSanitizerSettings
+{
+    public const string SectionName = "HtmlSanitizer";
+
+    /// <summary>
+    /// Gets or sets the list of HTML tags that are allowed.
+    /// If null or empty, the default allowed tags list is used.
+    /// </summary>
+    public List<string>? AllowedTags { get; set; }
+
+    /// <summary>
+    /// Gets or sets the list of HTML attributes that are allowed.
+    /// If null or empty, the default allowed attributes list is used.
+    /// </summary>
+    public List<string>? AllowedAttributes { get; set; }
+
+    /// <summary>
+    /// Gets or sets the list of CSS properties that are allowed.
+    /// If null or empty, the default allowed CSS properties list is used.
+    /// </summary>
+    public List<string>? AllowedCssProperties { get; set; }
+
+    /// <summary>
+    /// Gets or sets the list of URI schemes that are allowed (e.g. "http", "https").
+    /// If null or empty, the default allowed schemes list is used.
+    /// </summary>
+    public List<string>? AllowedSchemes { get; set; }
+}

src/NexusReader.Infrastructure/DependencyInjection.cs

@@ -78,6 +78,7 @@ public static class DependencyInjection
         services.Configure<AiSettings>(configuration.GetSection(AiSettings.SectionName));
         services.Configure<StripeSettings>(configuration.GetSection(StripeSettings.SectionName));
         services.Configure<RagMonetizationOptions>(configuration.GetSection(RagMonetizationOptions.SectionName));
+        services.Configure<HtmlSanitizerSettings>(configuration.GetSection(HtmlSanitizerSettings.SectionName));
         var aiSettings = configuration.GetSection(AiSettings.SectionName).Get<AiSettings>() ?? new AiSettings();
 
         if (string.IsNullOrWhiteSpace(aiSettings.ApiKey) || aiSettings.ApiKey == "PLACEHOLDER")
@@ -124,6 +125,8 @@ public static class DependencyInjection
         // Fix #4: Scoped instead of Singleton — BookStorageService uses path resolution
         // that is environment-specific and incompatible with Singleton lifetime in MAUI.
         services.AddScoped<IBookStorageService, BookStorageService>();
+        services.AddScoped<IStorageService, LocalStorageService>();
+        services.AddSingleton<ISanitizerService, HtmlSanitizerService>();
 
         // Fix #1: Ebook repository (scoped, matches AppDbContext lifetime)
         services.AddScoped<IEbookRepository, EbookRepository>();

src/NexusReader.Infrastructure/NexusReader.Infrastructure.csproj

@@ -28,6 +28,7 @@
     <PackageReference Include="Npgsql.EntityFrameworkCore.PostgreSQL" />
     <PackageReference Include="Polly" />
     <PackageReference Include="Polly.Extensions.Http" />
+    <PackageReference Include="HtmlSanitizer" />
     <PackageReference Include="Qdrant.Client" />
     <PackageReference Include="Stripe.net" />
     <PackageReference Include="VersOne.Epub" />

src/NexusReader.Infrastructure/Services/HtmlSanitizerService.cs

@@ -0,0 +1,70 @@
+using Ganss.Xss;
+using Microsoft.Extensions.Options;
+using NexusReader.Application.Abstractions.Services;
+using NexusReader.Infrastructure.Configuration;
+
+namespace NexusReader.Infrastructure.Services;
+
+/// <summary>
+/// Infrastructure implementation of ISanitizerService using the Ganss.Xss HtmlSanitizer library.
+/// </summary>
+public class HtmlSanitizerService : ISanitizerService
+{
+    private readonly HtmlSanitizer _sanitizer;
+
+    public HtmlSanitizerService(IOptions<HtmlSanitizerSettings>? options = null)
+    {
+        _sanitizer = new HtmlSanitizer();
+        
+        if (options?.Value != null)
+        {
+            var settings = options.Value;
+            
+            if (settings.AllowedTags != null && settings.AllowedTags.Count > 0)
+            {
+                _sanitizer.AllowedTags.Clear();
+                foreach (var tag in settings.AllowedTags)
+                {
+                    _sanitizer.AllowedTags.Add(tag);
+                }
+            }
+
+            if (settings.AllowedAttributes != null && settings.AllowedAttributes.Count > 0)
+            {
+                _sanitizer.AllowedAttributes.Clear();
+                foreach (var attr in settings.AllowedAttributes)
+                {
+                    _sanitizer.AllowedAttributes.Add(attr);
+                }
+            }
+
+            if (settings.AllowedCssProperties != null && settings.AllowedCssProperties.Count > 0)
+            {
+                _sanitizer.AllowedCssProperties.Clear();
+                foreach (var prop in settings.AllowedCssProperties)
+                {
+                    _sanitizer.AllowedCssProperties.Add(prop);
+                }
+            }
+
+            if (settings.AllowedSchemes != null && settings.AllowedSchemes.Count > 0)
+            {
+                _sanitizer.AllowedSchemes.Clear();
+                foreach (var scheme in settings.AllowedSchemes)
+                {
+                    _sanitizer.AllowedSchemes.Add(scheme);
+                }
+            }
+        }
+    }
+
+    public string Sanitize(string input)
+    {
+        if (string.IsNullOrEmpty(input))
+        {
+            return input;
+        }
+
+        return _sanitizer.Sanitize(input);
+    }
+}

src/NexusReader.Infrastructure/Services/LocalStorageService.cs

@@ -0,0 +1,58 @@
+using Microsoft.AspNetCore.Hosting;
+using NexusReader.Application.Abstractions.Services;
+
+namespace NexusReader.Infrastructure.Services;
+
+/// <summary>
+/// Infrastructure implementation of general storage utilizing local filesystem.
+/// Files are saved in wwwroot/uploads/media.
+/// </summary>
+public class LocalStorageService : IStorageService
+{
+    private readonly IWebHostEnvironment _environment;
+
+    public LocalStorageService(IWebHostEnvironment environment)
+    {
+        _environment = environment;
+    }
+
+    public async Task<string> UploadFileAsync(byte[] fileBytes, string fileName, string contentType)
+    {
+        using var stream = new MemoryStream(fileBytes);
+        return await UploadFileAsync(stream, fileName, contentType);
+    }
+
+    public async Task<string> UploadFileAsync(Stream fileStream, string fileName, string contentType)
+    {
+        var mediaFolder = Path.Combine(_environment.WebRootPath, "uploads", "media");
+        var resolvedMediaFolder = Path.GetFullPath(mediaFolder);
+        var folderWithSeparator = resolvedMediaFolder.EndsWith(Path.DirectorySeparatorChar)
+            ? resolvedMediaFolder
+            : resolvedMediaFolder + Path.DirectorySeparatorChar;
+        
+        if (!Directory.Exists(resolvedMediaFolder))
+        {
+            Directory.CreateDirectory(resolvedMediaFolder);
+        }
+
+        // Clean file name to prevent path traversal issues
+        var safeFileName = Path.GetFileName(fileName);
+        var uniqueFileName = $"{Guid.NewGuid()}_{safeFileName}";
+        var filePath = Path.Combine(resolvedMediaFolder, uniqueFileName);
+        
+        // Guard against path traversal
+        var fullPath = Path.GetFullPath(filePath);
+        if (!fullPath.StartsWith(folderWithSeparator, StringComparison.OrdinalIgnoreCase))
+        {
+            throw new InvalidOperationException("Path traversal detected.");
+        }
+
+        using (var outputStream = new FileStream(fullPath, FileMode.Create))
+        {
+            await fileStream.CopyToAsync(outputStream);
+        }
+
+        // Return the public web-relative URL
+        return $"/uploads/media/{uniqueFileName}";
+    }
+}

src/NexusReader.UI.Shared/Components/Atoms/NexusIcon.razor

@@ -101,6 +101,11 @@
                     <line x1="5" y1="12" x2="19" y2="12" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round" />
                     <polyline points="12 5 19 12 12 19" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round" />
             break;
+        case "edit":
+        case "edit-2":
+                    <path d="M11 4H4a2 2 0 0 0-2 2v14a2 2 0 0 0 2 2h14a2 2 0 0 0 2-2v-7" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round" />
+                    <path d="M18.5 2.5a2.121 2.121 0 1 1 3 3L12 15l-4 1 1-4 9.5-9.5z" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round" />
+            break;
         case "log-out":
                     <path d="M9 21H5a2 2 0 0 1-2-2V5a2 2 0 0 1 2-2h4M16 17l5-5-5-5M21 12H9" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round" />
             break;

src/NexusReader.UI.Shared/Components/MarkdownEditor.razor

@@ -0,0 +1,154 @@
+@using Microsoft.JSInterop
+@implements IAsyncDisposable
+@inject IJSRuntime JS
+@inject HttpClient Http
+
+<div class="markdown-editor-container" style="height: @Height; width: @Width;">
+    <div id="@EditorId" class="milkdown-editor-wrapper"></div>
+    @if (ShowFetchButton)
+    {
+        <div class="editor-actions">
+            <button type="button" @onclick="FetchContentAsync" class="nexus-btn">
+                Fetch Markdown Content
+            </button>
+        </div>
+    }
+</div>
+
+@code {
+    private readonly string EditorId = $"milkdown-editor-{Guid.NewGuid():N}";
+    private readonly CancellationTokenSource _cts = new();
+    private IJSObjectReference? _module;
+    private DotNetObjectReference<MarkdownEditor>? _dotNetHelper;
+
+    [Parameter]
+    public bool ShowFetchButton { get; set; } = true;
+
+    [Parameter]
+    public string InitialMarkdown { get; set; } = string.Empty;
+
+    [Parameter]
+    public EventCallback<string> OnSave { get; set; }
+
+    [Parameter]
+    public string Height { get; set; } = "500px";
+
+    [Parameter]
+    public string Width { get; set; } = "100%";
+
+    protected override async Task OnAfterRenderAsync(bool firstRender)
+    {
+        if (firstRender)
+        {
+            _dotNetHelper = DotNetObjectReference.Create(this);
+            try
+            {
+                // Import the isolated JavaScript module
+                _module = await JS.InvokeAsync<IJSObjectReference>(
+                    "import", 
+                    "./_content/NexusReader.UI.Shared/js/milkdownWrapper.js"
+                );
+
+                // Call the initialization function in the wrapper
+                await _module.InvokeVoidAsync("initEditor", EditorId, _dotNetHelper, InitialMarkdown);
+            }
+            catch (Exception ex)
+            {
+                // Log the exception gracefully and do not crash the component
+                Console.WriteLine($"[MarkdownEditor] Error initializing Milkdown editor: {ex.Message}");
+            }
+        }
+    }
+
+    public async Task FetchContentAsync()
+    {
+        if (_module is not null)
+        {
+            try
+            {
+                // Retrieve the updated markdown from JS
+                var markdown = await _module.InvokeAsync<string>("getMarkdownContent", EditorId);
+                
+                if (OnSave.HasDelegate)
+                {
+                    await OnSave.InvokeAsync(markdown);
+                }
+            }
+            catch (Exception ex)
+            {
+                Console.WriteLine($"[MarkdownEditor] Error fetching markdown content: {ex.Message}");
+            }
+        }
+    }
+
+    [JSInvokable]
+    public async Task<string> UploadImageFromJs(string filename, string contentType, byte[] fileBytes)
+    {
+        try
+        {
+            using var content = new MultipartFormDataContent();
+            var fileContent = new ByteArrayContent(fileBytes);
+            fileContent.Headers.ContentType = new System.Net.Http.Headers.MediaTypeHeaderValue(contentType);
+            content.Add(fileContent, "file", filename);
+
+            var response = await Http.PostAsync("/api/media/upload", content, _cts.Token);
+            if (response.IsSuccessStatusCode)
+            {
+                var result = await response.Content.ReadFromJsonAsync<NexusReader.Application.DTOs.Media.UploadResultDto>(
+                    NexusReader.Application.Common.AppJsonContext.Default.UploadResultDto, _cts.Token);
+                return result?.Url ?? string.Empty;
+            }
+            else
+            {
+                var errorMsg = await response.Content.ReadAsStringAsync();
+                Console.WriteLine($"[MarkdownEditor] Image upload failed: {response.StatusCode} - {errorMsg}");
+                return string.Empty;
+            }
+        }
+        catch (Exception ex)
+        {
+            Console.WriteLine($"[MarkdownEditor] Exception during image upload: {ex.Message}");
+            return string.Empty;
+        }
+    }
+
+    public async ValueTask DisposeAsync()
+    {
+        try
+        {
+            _cts.Cancel();
+            _cts.Dispose();
+        }
+        catch
+        {
+            // Fail silently if cancellation token disposal fails
+        }
+
+        try
+        {
+            if (_module is not null)
+            {
+                // Clean up the JS editor instance to prevent memory leaks
+                await _module.InvokeVoidAsync("destroyEditor", EditorId);
+                await _module.DisposeAsync();
+            }
+        }
+        catch (JSDisconnectedException)
+        {
+            // Fail silently during circuit disconnection
+        }
+        catch (ObjectDisposedException)
+        {
+            // Fail silently if JS runtime/module is already disposed
+        }
+        catch (Exception ex)
+        {
+            // Log other unexpected errors
+            Console.WriteLine($"[MarkdownEditor] Unexpected error during JS cleanup: {ex.Message}");
+        }
+        finally
+        {
+            _dotNetHelper?.Dispose();
+        }
+    }
+}

src/NexusReader.UI.Shared/Components/MarkdownEditor.razor.css

@@ -0,0 +1,86 @@
+.markdown-editor-container {
+    display: flex;
+    flex-direction: column;
+    gap: 1rem;
+}
+
+.milkdown-editor-wrapper {
+    flex: 1;
+    border: 1px solid var(--border);
+    border-radius: var(--radius-md);
+    background: var(--bg-surface);
+    overflow: auto;
+    padding: 1.5rem;
+    position: relative;
+    transition: border-color 0.2s ease, box-shadow 0.2s ease;
+}
+
+.milkdown-editor-wrapper:focus-within {
+    border-color: var(--accent);
+    box-shadow: 0 0 0 1px var(--accent-glow);
+}
+
+.editor-actions {
+    display: flex;
+    justify-content: flex-end;
+}
+
+/* 3. Bypassing Blazor CSS Isolation for Dynamic JS DOMs using ::deep */
+::deep .milkdown-editor-wrapper .crepe {
+    max-width: 100% !important;
+}
+
+::deep .milkdown-editor-wrapper .milkdown {
+    background-color: var(--bg-surface) !important;
+    color: var(--text-main) !important;
+    font-family: var(--nexus-font-sans) !important;
+    border: none !important;
+    box-shadow: none !important;
+    
+    /* Map Crepe's internal variables to our design tokens */
+    --crepe-color-background: var(--bg-surface);
+    --crepe-color-on-background: var(--text-main);
+    --crepe-color-surface: rgba(255, 255, 255, 0.03);
+    --crepe-color-surface-low: rgba(255, 255, 255, 0.01);
+    --crepe-color-primary: var(--accent);
+    --crepe-color-outline: var(--border);
+}
+
+::deep .milkdown-editor-wrapper .milkdown .editor {
+    color: var(--text-main) !important;
+    background: transparent !important;
+    outline: none !important;
+    padding: 0.5rem 0 !important;
+    min-height: 200px;
+}
+
+/* Style the buttons using variables from app.css */
+.nexus-btn {
+    font-family: var(--nexus-font-sans);
+    font-weight: 600;
+    border-radius: var(--radius-md);
+    transition: all 0.2s cubic-bezier(0.4, 0, 0.2, 1);
+    cursor: pointer;
+    display: inline-flex;
+    align-items: center;
+    justify-content: center;
+    gap: 0.5rem;
+    border: none;
+    text-decoration: none;
+    background: var(--nexus-neon);
+    color: #000000;
+    padding: 8px 16px;
+    font-size: 0.9rem;
+    min-height: 36px;
+}
+
+.nexus-btn:hover {
+    transform: translateY(-2px);
+    filter: brightness(1.1);
+    box-shadow: 0 4px 15px var(--nexus-primary-glow);
+}
+
+.nexus-btn:focus-visible {
+    outline: 2px solid var(--accent);
+    outline-offset: 2px;
+}

src/NexusReader.UI.Shared/Layout/MainHubLayout.razor

@@ -95,6 +95,12 @@
                         </div>
                         <span class="nav-text">Koncentry</span>
                     </NavLink>
+                    <NavLink class="nav-item" href="/creator" @onclick="CloseMobileMenu" title="Kreator" aria-label="Kreator">
+                        <div class="nav-icon">
+                            <NexusIcon Name="edit" Size="20" />
+                        </div>
+                        <span class="nav-text">Kreator</span>
+                    </NavLink>
                 </nav>
 
                 <div class="sidebar-footer">

src/NexusReader.UI.Shared/Pages/Creator.razor

@@ -0,0 +1,76 @@
+@page "/creator"
+@using Microsoft.AspNetCore.Authorization
+@attribute [Authorize]
+
+<PageTitle>Kreator Treści (Zen Mode)</PageTitle>
+
+<div class="creator-fullscreen-wrapper">
+    <div class="creator-header">
+        <h1>Kreator Treści</h1>
+        <p class="subtitle">Zen publishing workspace mapping standard Markdown into clean visual blocks.</p>
+    </div>
+
+    <div class="milkdown-premium-container creator-workspace-card" spellcheck="false">
+        <div class="editor-growing-area">
+            <MarkdownEditor @ref="_editorRef" InitialMarkdown="@_initialMarkdown" OnSave="HandleSave" ShowFetchButton="false" Height="100%" />
+        </div>
+        
+        <div class="creator-actions-bar">
+            <button type="button" @onclick="TriggerFetchAsync" class="nexus-btn premium-fetch-btn btn-nexus-premium">
+                <span>Fetch Markdown Content</span>
+                <svg class="arrow-icon" viewBox="0 0 24 24" width="16" height="16" stroke="currentColor" stroke-width="2.5" fill="none" stroke-linecap="round" stroke-linejoin="round">
+                    <line x1="5" y1="12" x2="19" y2="12"></line>
+                    <polyline points="12 5 19 12 12 19"></polyline>
+                </svg>
+            </button>
+        </div>
+    </div>
+
+    @if (!string.IsNullOrEmpty(_savedMarkdown))
+    {
+        <div class="creator-preview-card">
+            <div class="preview-header">
+                <h3>Retrieved Markdown Preview</h3>
+            </div>
+            <div class="pre-wrapper">
+                <pre class="code-preview-block"><code>@_savedMarkdown</code></pre>
+            </div>
+        </div>
+    }
+</div>
+
+@code {
+    private MarkdownEditor? _editorRef;
+    private string _savedMarkdown = string.Empty;
+
+    private readonly string _initialMarkdown = @"# Zen Mode Editor
+
+Welcome to your dedicated workspace. This premium panel supports Notion-like WYSIWYG editing.
+
+## Features:
+- **Zero Distraction**: Simple elevation and border framing.
+- **GFM Tables**: Consistent cell padding and hover striping.
+- **Clean Code Blocks**: Pre-rendered base64 font-loaded code-preview blocks.
+
+| Option | Active | Value |
+| :--- | :---: | :--- |
+| Zen Mode | Yes | High Focus |
+| Responsive | Yes | 1200px Max |
+| Theme Sync | Yes | Automatic |
+
+Start writing your masterpiece...";
+
+    private async Task TriggerFetchAsync()
+    {
+        if (_editorRef is not null)
+        {
+            await _editorRef.FetchContentAsync();
+        }
+    }
+
+    private void HandleSave(string markdown)
+    {
+        _savedMarkdown = markdown;
+        StateHasChanged();
+    }
+}

src/NexusReader.UI.Shared/Pages/Creator.razor.css

@@ -0,0 +1,349 @@
+/* ==========================================================================
+   Creator.razor.css - Isolated Styles for Zen Mode Creator Workspace
+   ========================================================================== */
+
+/* 1. BOUNDARY & SCROLLING RE-ENGINEERING */
+
+/* Strict flexbox layout context eliminating global browser scrollbars */
+.creator-fullscreen-wrapper {
+    width: 100% !important;
+    max-width: 100% !important; /* Likwidujemy sztuczne ograniczenia szerokości */
+    margin: 0;
+    padding: 1.5rem; /* Elastyczny, bezpieczny margines od krawędzi bocznych menu i ekranu */
+    display: flex;
+    flex-direction: column;
+    height: calc(100vh - 4rem); 
+    box-sizing: border-box;
+    overflow: hidden;
+    gap: 1.25rem;
+}
+
+.creator-header {
+    flex-shrink: 0;
+    padding-left: 0.5rem;
+}
+
+.creator-header h1 {
+    font-size: 1.75rem;
+    font-weight: 700;
+    color: var(--text-main);
+    margin: 0 0 0.25rem 0;
+}
+
+.creator-header .subtitle {
+    font-size: 0.9rem;
+    color: var(--text-muted);
+    margin: 0;
+}
+
+/* 2. Full Viewport Workspace Card stretching smoothly */
+.creator-workspace-card {
+    background-color: var(--bg-surface) !important;
+    border: 1px solid var(--border) !important;
+    border-radius: 20px;
+    padding: 2rem;
+    box-shadow: 0 12px 40px rgba(0, 0, 0, 0.2);
+    display: flex;
+    flex-direction: column;
+    flex-grow: 1; 
+    width: 100% !important;
+    box-sizing: border-box;
+    overflow: hidden; 
+}
+
+.editor-growing-area {
+    flex-grow: 1;
+    display: flex;
+    flex-direction: column;
+    overflow: hidden;
+}
+
+/* 3. Deep Cascading Overrides to target dynamic editor components */
+
+.creator-fullscreen-wrapper ::deep .markdown-editor-container {
+    height: 100% !important;
+    display: flex !important;
+    flex-direction: column !important;
+    flex-grow: 1 !important;
+    overflow: hidden !important;
+}
+
+.creator-fullscreen-wrapper ::deep .milkdown-editor-wrapper {
+    display: flex !important;
+    flex-direction: column !important;
+    flex-grow: 1 !important;
+    overflow: hidden !important;
+}
+
+/* Force crepe and milkdown inner wrappers to stretch */
+.creator-fullscreen-wrapper ::deep .crepe,
+.creator-fullscreen-wrapper ::deep .milkdown {
+    width: 100% !important;
+    max-width: 100% !important;
+    display: flex !important;
+    flex-direction: column !important;
+    flex-grow: 1 !important;
+    overflow: hidden !important;
+    background-color: transparent !important;
+    background: transparent !important;
+}
+
+/* Pin the toolbar at the top */
+.creator-fullscreen-wrapper ::deep .crepe .toolbar,
+.creator-fullscreen-wrapper ::deep .milkdown-menu,
+.creator-fullscreen-wrapper ::deep .crepe-menu-wrapper {
+    flex-shrink: 0 !important;
+    background-color: var(--bg-base) !important;
+    border: 1px solid var(--border) !important;
+    border-radius: 12px !important;
+    padding: 0.5rem !important;
+    margin-bottom: 1rem !important;
+}
+
+.creator-fullscreen-wrapper ::deep .crepe .toolbar button:hover,
+.creator-fullscreen-wrapper ::deep .milkdown-menu button:hover,
+.creator-fullscreen-wrapper ::deep .crepe-menu-wrapper button:hover,
+.creator-fullscreen-wrapper ::deep .crepe .toolbar .button:hover,
+.creator-fullscreen-wrapper ::deep .milkdown-menu .button:hover {
+    color: var(--accent) !important;
+    background-color: rgba(16, 185, 129, 0.1) !important;
+    border-radius: var(--radius-sm, 4px) !important;
+}
+
+/* Relocate scrolling directly to ProseMirror editor layer and fix text clipping */
+.creator-fullscreen-wrapper ::deep .ProseMirror,
+.creator-fullscreen-wrapper ::deep .crepe .editor,
+.creator-fullscreen-wrapper ::deep .milkdown .editor {
+    position: relative !important;
+    top: 0 !important;
+    transform: none !important;
+    flex-grow: 1 !important;
+    overflow-y: auto !important;
+    padding: 1.5rem !important;
+    padding-right: 15px !important;
+    background-color: var(--bg-surface) !important;
+    color: var(--text-main) !important;
+    font-size: 1.1rem !important;
+    line-height: 1.7 !important;
+    outline: none !important;
+    width: 100% !important;
+    max-width: 100% !important;
+}
+
+/* Custom narrow scrollbar mapped to var(--border) */
+.creator-fullscreen-wrapper ::deep .ProseMirror::-webkit-scrollbar,
+.creator-fullscreen-wrapper ::deep .crepe .editor::-webkit-scrollbar,
+.creator-fullscreen-wrapper ::deep .milkdown .editor::-webkit-scrollbar {
+    width: 6px;
+    height: 6px;
+}
+
+.creator-fullscreen-wrapper ::deep .ProseMirror::-webkit-scrollbar-track,
+.creator-fullscreen-wrapper ::deep .crepe .editor::-webkit-scrollbar-track,
+.creator-fullscreen-wrapper ::deep .milkdown .editor::-webkit-scrollbar-track {
+    background: transparent;
+}
+
+.creator-fullscreen-wrapper ::deep .ProseMirror::-webkit-scrollbar-thumb,
+.creator-fullscreen-wrapper ::deep .crepe .editor::-webkit-scrollbar-thumb,
+.creator-fullscreen-wrapper ::deep .milkdown .editor::-webkit-scrollbar-thumb {
+    background: var(--border);
+    border-radius: 3px;
+}
+
+.creator-fullscreen-wrapper ::deep .ProseMirror::-webkit-scrollbar-thumb:hover,
+.creator-fullscreen-wrapper ::deep .crepe .editor::-webkit-scrollbar-thumb:hover,
+.creator-fullscreen-wrapper ::deep .milkdown .editor::-webkit-scrollbar-thumb:hover {
+    background: var(--text-muted);
+}
+
+/* Editorial Typography */
+.creator-fullscreen-wrapper ::deep .milkdown .editor h1,
+.creator-fullscreen-wrapper ::deep .crepe h1,
+.creator-fullscreen-wrapper ::deep .ProseMirror h1 {
+    margin-top: 1.8rem !important;
+    margin-bottom: 1rem !important;
+    font-size: 2.25rem !important;
+    font-weight: 700 !important;
+    color: var(--text-main) !important;
+    line-height: 1.25 !important;
+}
+
+.creator-fullscreen-wrapper ::deep .milkdown .editor h2,
+.creator-fullscreen-wrapper ::deep .crepe h2,
+.creator-fullscreen-wrapper ::deep .ProseMirror h2 {
+    margin-top: 1.5rem !important;
+    margin-bottom: 0.8rem !important;
+    font-size: 1.6rem !important;
+    font-weight: 700 !important;
+    color: var(--text-main) !important;
+    line-height: 1.3 !important;
+}
+
+.creator-fullscreen-wrapper ::deep .milkdown .editor h3,
+.creator-fullscreen-wrapper ::deep .crepe h3,
+.creator-fullscreen-wrapper ::deep .ProseMirror h3 {
+    margin-top: 1.3rem !important;
+    margin-bottom: 0.7rem !important;
+    font-size: 1.3rem !important;
+    font-weight: 700 !important;
+    color: var(--text-main) !important;
+    line-height: 1.35 !important;
+}
+
+.creator-fullscreen-wrapper ::deep .milkdown .editor code,
+.creator-fullscreen-wrapper ::deep .crepe code,
+.creator-fullscreen-wrapper ::deep .ProseMirror code {
+    background-color: rgba(16, 185, 129, 0.1) !important;
+    color: var(--accent) !important;
+    padding: 0.2rem 0.4rem !important;
+    border-radius: var(--radius-sm, 4px) !important;
+    font-family: var(--nexus-font-mono) !important;
+    font-size: 0.85em !important;
+}
+
+/* Premium GFM Table Layouts */
+.creator-fullscreen-wrapper ::deep .milkdown-premium-container table,
+.creator-fullscreen-wrapper ::deep .crepe table,
+.creator-fullscreen-wrapper ::deep .milkdown table,
+.creator-fullscreen-wrapper ::deep .ProseMirror table {
+    width: 100% !important;
+    max-width: 100% !important;
+    border-collapse: collapse !important;
+    margin: 1.5rem 0 !important;
+}
+
+.creator-fullscreen-wrapper ::deep .milkdown-premium-container th,
+.creator-fullscreen-wrapper ::deep .crepe th,
+.creator-fullscreen-wrapper ::deep .milkdown th,
+.creator-fullscreen-wrapper ::deep .ProseMirror th,
+.creator-fullscreen-wrapper ::deep .milkdown-premium-container td,
+.creator-fullscreen-wrapper ::deep .crepe td,
+.creator-fullscreen-wrapper ::deep .milkdown td,
+.creator-fullscreen-wrapper ::deep .ProseMirror td {
+    padding: 14px 18px !important;
+    border: 1px solid var(--border) !important;
+}
+
+.creator-fullscreen-wrapper ::deep .milkdown-premium-container th,
+.creator-fullscreen-wrapper ::deep .crepe th,
+.creator-fullscreen-wrapper ::deep .milkdown th,
+.creator-fullscreen-wrapper ::deep .ProseMirror th {
+    background-color: var(--bg-base) !important;
+    color: var(--text-main) !important;
+    font-weight: 700 !important;
+    text-align: left !important;
+}
+
+.creator-fullscreen-wrapper ::deep .milkdown-premium-container td,
+.creator-fullscreen-wrapper ::deep .crepe td,
+.creator-fullscreen-wrapper ::deep .milkdown td,
+.creator-fullscreen-wrapper ::deep .ProseMirror td {
+    color: var(--text-main) !important;
+}
+
+/* Zebra row background tints (Dark Mode default) */
+.creator-fullscreen-wrapper ::deep .milkdown-premium-container tr:nth-child(even),
+.creator-fullscreen-wrapper ::deep .crepe tr:nth-child(even),
+.creator-fullscreen-wrapper ::deep .milkdown tr:nth-child(even),
+.creator-fullscreen-wrapper ::deep .ProseMirror tr:nth-child(even) {
+    background-color: rgba(255, 255, 255, 0.01) !important;
+}
+
+/* Zebra row background tints (Light Mode override) */
+.theme-light .creator-fullscreen-wrapper ::deep .milkdown-premium-container tr:nth-child(even),
+.theme-light .creator-fullscreen-wrapper ::deep .crepe tr:nth-child(even),
+.theme-light .creator-fullscreen-wrapper ::deep .milkdown tr:nth-child(even),
+.theme-light .creator-fullscreen-wrapper ::deep .ProseMirror tr:nth-child(even) {
+    background-color: rgba(0, 0, 0, 0.015) !important;
+}
+
+/* Lists and Task Lists */
+.creator-fullscreen-wrapper ::deep .crepe ul,
+.creator-fullscreen-wrapper ::deep .crepe ol,
+.creator-fullscreen-wrapper ::deep .milkdown ul,
+.creator-fullscreen-wrapper ::deep .milkdown ol,
+.creator-fullscreen-wrapper ::deep .ProseMirror ul,
+.creator-fullscreen-wrapper ::deep .ProseMirror ol {
+    line-height: 1.7 !important;
+}
+
+/* 4. Bottom Actions Panel locked at floor zone of the card structure */
+.creator-actions-bar {
+    display: flex;
+    justify-content: flex-end; 
+    margin-top: 1.5rem;
+    padding: 1rem 0 0 0;
+    border-top: 1px solid var(--border);
+    flex-shrink: 0;
+    width: 100%;
+}
+
+.btn-nexus-premium {
+    display: inline-flex;
+    align-items: center;
+    gap: 0.5rem;
+    transition: all 0.2s cubic-bezier(0.4, 0, 0.2, 1);
+    background-color: var(--accent) !important;
+    background: var(--accent) !important;
+    color: #000000 !important;
+    border: none;
+    border-radius: var(--radius-md);
+    padding: 8px 16px;
+    font-weight: 600;
+    cursor: pointer;
+    font-family: var(--nexus-font-sans);
+    font-size: 0.9rem;
+    min-height: 36px;
+}
+
+.btn-nexus-premium:hover {
+    transform: translateY(-2px);
+    filter: brightness(1.1);
+    box-shadow: 0 4px 15px var(--accent-glow);
+}
+
+.btn-nexus-premium:hover .arrow-icon {
+    transform: translateX(4px);
+}
+
+.arrow-icon {
+    transition: transform 0.2s ease;
+}
+
+/* 5. Dedicated Preview Card */
+.creator-preview-card {
+    background: #121214;
+    border: 1px solid rgba(255, 255, 255, 0.08);
+    border-radius: var(--radius-lg);
+    padding: 1.25rem;
+    flex-shrink: 0;
+    max-height: 180px;
+    display: flex;
+    flex-direction: column;
+    box-shadow: 0 8px 25px rgba(0, 0, 0, 0.25);
+}
+
+.preview-header h3 {
+    margin: 0 0 0.75rem 0;
+    font-size: 1.1rem;
+    font-weight: 600;
+    color: #ffffff;
+    font-family: var(--nexus-font-sans);
+}
+
+.pre-wrapper {
+    overflow-y: auto;
+    overflow-x: auto;
+    flex-grow: 1;
+}
+
+.code-preview-block {
+    margin: 0;
+    white-space: pre-wrap;
+    word-break: break-all;
+    font-family: 'Azeret Mono', SFMono-Regular, Consolas, Menlo, monospace;
+    font-size: 0.85rem;
+    color: #e4e4e7;
+    line-height: 1.6;
+}

src/NexusReader.UI.Shared/wwwroot/app.css

@@ -1,4 +1,4 @@
-@import url('https://fonts.googleapis.com/css2?family=Inter:wght@400;500;600&family=Merriweather:ital,wght@0,300;0,400;0,700;1,400&display=swap');
+@import url('https://fonts.googleapis.com/css2?family=Inter:wght@400;500;600&family=Merriweather:ital,wght@0,300;0,400;0,700;1,400&family=Azeret+Mono:wght@300;400;500;600&display=swap');
 
 :root {
     /* Semantic design tokens - default to Modern Deep Dark (Dark Mode) */
@@ -19,6 +19,7 @@
     --nexus-paper: #F9F9F9;
     --nexus-font-sans: 'Inter', sans-serif;
     --nexus-font-serif: 'Merriweather', serif;
+    --nexus-font-mono: 'Azeret Mono', monospace;
 
     /* Global Selection Style Override */
     --nexus-selection: rgba(0, 255, 153, 0.25);
@@ -60,9 +61,12 @@
     --nexus-node-concept-text: #e0e0e0;
 }
 
-::selection {
-    background-color: var(--nexus-selection);
-    color: inherit;
+::selection,
+.ProseMirror ::selection,
+.ProseMirror::selection,
+.ProseMirror *::selection {
+    background-color: var(--nexus-selection) !important;
+    color: inherit !important;
 }
 
 
@@ -444,4 +448,547 @@ h1:focus {
         opacity: 0.5;
         transform: scale(0.95);
     }
-}
+}
+
+/* ==========================================================================
+   Selection Pop-up Menu & Crepe Toolbar Unification (SelectionAiPanel Style)
+   ========================================================================== */
+
+/* 1. Pop-up Containers (Glassmorphism Capsule) */
+.milkdown-popover,
+.popover,
+.prosemirror-bubble-menu,
+.milkdown .popover,
+.milkdown-popover.popover,
+.milkdown-toolbar {
+    background: rgba(24, 24, 28, 0.85) !important;
+    backdrop-filter: blur(12px) !important;
+    -webkit-backdrop-filter: blur(12px) !important;
+    border: 1px solid rgba(255, 255, 255, 0.08) !important;
+    border-radius: 8px !important;
+    padding: 4px 6px !important;
+    margin: 0 !important;
+    box-shadow: 0 4px 12px rgba(0, 0, 0, 0.5), 0 12px 28px rgba(0, 0, 0, 0.4) !important;
+    display: inline-flex; /* Removed !important to allow Tippy.js to hide popovers via inline style */
+    align-items: center !important;
+    gap: 4px !important;
+    z-index: 10000 !important;
+    box-sizing: border-box !important;
+    animation: fadeInScaleGlobal 0.18s cubic-bezier(0.16, 1, 0.3, 1) !important;
+}
+
+/* Light Theme (Warm Paper) Overrides for Container */
+.theme-light .milkdown-popover,
+.theme-light .popover,
+.theme-light .prosemirror-bubble-menu,
+.theme-light .milkdown .popover,
+.theme-light .milkdown-popover.popover,
+.theme-light .milkdown-toolbar {
+    background: rgba(254, 254, 254, 0.95) !important;
+    border: 1px solid rgba(0, 0, 0, 0.08) !important;
+    box-shadow: 0 4px 20px rgba(0, 0, 0, 0.05), 0 10px 30px rgba(0, 0, 0, 0.04) !important;
+}
+
+/* 2. Button & Item Formatting (Reader Selection Toolbar Style) */
+.milkdown-popover button,
+.popover button,
+.prosemirror-bubble-menu button,
+.milkdown .popover button,
+.milkdown-toolbar button {
+    text-transform: none !important;
+    font-size: 0.8rem !important;
+    font-weight: 500 !important;
+    color: #e4e4e7 !important; /* zinc-200 */
+    background: transparent !important;
+    border: none !important;
+    padding: 6px 12px !important;
+    margin: 0 !important;
+    border-radius: 6px !important;
+    transition: all 0.2s cubic-bezier(0.4, 0, 0.2, 1) !important;
+    display: inline-flex !important;
+    align-items: center !important;
+    justify-content: center !important;
+    cursor: pointer !important;
+    gap: 6px !important;
+}
+
+/* Crepe's Specific Square Icon-Only Toolbar Items */
+.milkdown-toolbar .toolbar-item {
+    text-transform: none !important;
+    color: #e4e4e7 !important; /* zinc-200 */
+    background: transparent !important;
+    border: none !important;
+    margin: 0 !important;
+    border-radius: 6px !important;
+    transition: all 0.2s cubic-bezier(0.4, 0, 0.2, 1) !important;
+    cursor: pointer !important;
+    width: 28px !important;
+    height: 28px !important;
+    padding: 6px !important;
+    display: inline-flex !important;
+    justify-content: center !important;
+    align-items: center !important;
+    box-sizing: border-box !important;
+}
+
+/* Icon overrides inside buttons */
+.milkdown-popover button svg,
+.popover button svg,
+.prosemirror-bubble-menu button svg,
+.milkdown .popover button svg,
+.milkdown-popover button i,
+.popover button i,
+.prosemirror-bubble-menu button i,
+.milkdown .popover button i,
+.milkdown-toolbar button svg,
+.milkdown-toolbar .toolbar-item svg,
+.milkdown-toolbar button i,
+.milkdown-toolbar .toolbar-item i {
+    color: currentColor !important;
+    fill: currentColor !important;
+    width: 14px !important;
+    height: 14px !important;
+}
+
+/* Hover effects (zinc-200 / zinc-100 highlight) */
+.milkdown-popover button:hover:not(.active),
+.popover button:hover:not(.active),
+.prosemirror-bubble-menu button:hover:not(.active),
+.milkdown-toolbar button:hover:not(.active),
+.milkdown-toolbar .toolbar-item:hover:not(.active) {
+    background: rgba(255, 255, 255, 0.05) !important;
+    color: #ffffff !important;
+}
+
+/* Active formatting state colors (var(--accent, #00ff99)) */
+.milkdown-popover button.active,
+.popover button.active,
+.prosemirror-bubble-menu button.active,
+.milkdown-popover button[aria-pressed="true"],
+.popover button[aria-pressed="true"],
+.prosemirror-bubble-menu button[aria-pressed="true"],
+.milkdown-toolbar button.active,
+.milkdown-toolbar .toolbar-item.active,
+.milkdown-toolbar button[aria-pressed="true"],
+.milkdown-toolbar .toolbar-item[aria-pressed="true"] {
+    color: var(--accent, #00ff99) !important;
+}
+
+.milkdown-popover button.active:hover,
+.popover button.active:hover,
+.prosemirror-bubble-menu button.active:hover,
+.milkdown-popover button[aria-pressed="true"]:hover,
+.popover button[aria-pressed="true"]:hover,
+.prosemirror-bubble-menu button[aria-pressed="true"]:hover,
+.milkdown-toolbar button.active:hover,
+.milkdown-toolbar .toolbar-item.active:hover,
+.milkdown-toolbar button[aria-pressed="true"]:hover,
+.milkdown-toolbar .toolbar-item[aria-pressed="true"]:hover {
+    background: rgba(0, 255, 153, 0.08) !important;
+    box-shadow: 0 0 12px rgba(0, 255, 153, 0.15) !important;
+    color: var(--accent, #00ff99) !important;
+}
+
+/* 3. Light Theme Overrides for Buttons */
+.theme-light .milkdown-popover button,
+.theme-light .popover button,
+.theme-light .prosemirror-bubble-menu button,
+.theme-light .milkdown-toolbar button,
+.theme-light .milkdown-toolbar .toolbar-item {
+    color: #57524e !important;
+}
+
+.theme-light .milkdown-popover button:hover:not(.active),
+.theme-light .popover button:hover:not(.active),
+.theme-light .prosemirror-bubble-menu button:hover:not(.active),
+.theme-light .milkdown-toolbar button:hover:not(.active),
+.theme-light .milkdown-toolbar .toolbar-item:hover:not(.active) {
+    background: rgba(0, 0, 0, 0.04) !important;
+    color: #1c1917 !important;
+}
+
+.theme-light .milkdown-popover button.active,
+.theme-light .popover button.active,
+.theme-light .prosemirror-bubble-menu button.active,
+.theme-light .milkdown-popover button[aria-pressed="true"],
+.theme-light .popover button[aria-pressed="true"],
+.theme-light .prosemirror-bubble-menu button[aria-pressed="true"],
+.theme-light .milkdown-toolbar button.active,
+.theme-light .milkdown-toolbar .toolbar-item.active,
+.theme-light .milkdown-toolbar button[aria-pressed="true"],
+.theme-light .milkdown-toolbar .toolbar-item[aria-pressed="true"] {
+    color: #10b981 !important;
+}
+
+.theme-light .milkdown-popover button.active:hover,
+.theme-light .popover button.active:hover,
+.theme-light .prosemirror-bubble-menu button.active:hover,
+.theme-light .milkdown-popover button[aria-pressed="true"]:hover,
+.theme-light .popover button[aria-pressed="true"]:hover,
+.theme-light .prosemirror-bubble-menu button[aria-pressed="true"]:hover,
+.theme-light .milkdown-toolbar button.active:hover,
+.theme-light .milkdown-toolbar .toolbar-item.active:hover,
+.theme-light .milkdown-toolbar button[aria-pressed="true"]:hover,
+.theme-light .milkdown-toolbar .toolbar-item[aria-pressed="true"]:hover {
+    background: rgba(16, 185, 129, 0.06) !important;
+    box-shadow: 0 0 12px rgba(16, 185, 129, 0.1) !important;
+    color: #10b981 !important;
+}
+
+/* 4. Dividers Alignment */
+.milkdown-popover .divider,
+.popover .divider,
+.prosemirror-bubble-menu .divider,
+.milkdown .popover .divider,
+.milkdown-toolbar .divider {
+    width: 1px !important;
+    height: 16px !important;
+    background-color: rgba(255, 255, 255, 0.1) !important;
+    margin: 0 4px !important;
+    border: none !important;
+}
+
+.theme-light .milkdown-popover .divider,
+.theme-light .popover .divider,
+.theme-light .prosemirror-bubble-menu .divider,
+.theme-light .milkdown-toolbar .divider {
+    background-color: rgba(0, 0, 0, 0.08) !important;
+}
+
+    to {
+        opacity: 1;
+        transform: scale(1);
+    }
+}
+
+/* ==========================================================================
+   Editor Table & General Control Elements Theming (SelectionAiPanel Style)
+   ========================================================================== */
+
+/* 1. Cell Drag Handles (Column and Row Drag Handles) */
+.milkdown .milkdown-table-block .cell-handle {
+    background-color: rgba(24, 24, 28, 0.85) !important;
+    backdrop-filter: blur(12px) !important;
+    -webkit-backdrop-filter: blur(12px) !important;
+    border: 1px solid rgba(255, 255, 255, 0.08) !important;
+    box-shadow: 0 4px 12px rgba(0, 0, 0, 0.3) !important;
+    color: #e4e4e7 !important;
+    transition: all 0.2s ease !important;
+}
+
+.theme-light .milkdown .milkdown-table-block .cell-handle {
+    background-color: rgba(254, 254, 254, 0.95) !important;
+    border: 1px solid rgba(0, 0, 0, 0.08) !important;
+    color: #57524e !important;
+    box-shadow: 0 4px 12px rgba(0, 0, 0, 0.05) !important;
+}
+
+.milkdown .milkdown-table-block .cell-handle:hover {
+    background-color: rgba(255, 255, 255, 0.15) !important;
+    color: #ffffff !important;
+    border-color: var(--accent) !important;
+}
+
+.theme-light .milkdown .milkdown-table-block .cell-handle:hover {
+    background-color: rgba(0, 0, 0, 0.08) !important;
+    color: #1c1917 !important;
+    border-color: #10b981 !important;
+}
+
+.milkdown .milkdown-table-block .cell-handle svg {
+    fill: currentColor !important;
+    color: currentColor !important;
+}
+
+/* 2. Drag Handle Options Popup Menu (.button-group) */
+.milkdown .milkdown-table-block .cell-handle .button-group {
+    background: rgba(24, 24, 28, 0.85) !important;
+    backdrop-filter: blur(12px) !important;
+    -webkit-backdrop-filter: blur(12px) !important;
+    border: 1px solid rgba(255, 255, 255, 0.08) !important;
+    border-radius: 8px !important;
+    box-shadow: 0 4px 12px rgba(0, 0, 0, 0.5), 0 12px 28px rgba(0, 0, 0, 0.4) !important;
+    padding: 4px !important;
+    gap: 4px !important;
+    display: flex; /* Removed !important to allow toggling via data-show attribute */
+}
+
+.theme-light .milkdown .milkdown-table-block .cell-handle .button-group {
+    background: rgba(254, 254, 254, 0.95) !important;
+    border: 1px solid rgba(0, 0, 0, 0.08) !important;
+    box-shadow: 0 4px 20px rgba(0, 0, 0, 0.05), 0 10px 30px rgba(0, 0, 0, 0.04) !important;
+}
+
+.milkdown .milkdown-table-block .cell-handle .button-group button {
+    background: transparent !important;
+    border: none !important;
+    margin: 0 !important;
+    border-radius: 6px !important;
+    transition: all 0.2s cubic-bezier(0.4, 0, 0.2, 1) !important;
+    cursor: pointer !important;
+    width: 28px !important;
+    height: 28px !important;
+    padding: 6px !important;
+    display: inline-flex !important;
+    justify-content: center !important;
+    align-items: center !important;
+    box-sizing: border-box !important;
+    color: #e4e4e7 !important;
+}
+
+.theme-light .milkdown .milkdown-table-block .cell-handle .button-group button {
+    color: #57524e !important;
+}
+
+.milkdown .milkdown-table-block .cell-handle .button-group button:hover {
+    background: rgba(255, 255, 255, 0.05) !important;
+    color: #ffffff !important;
+}
+
+.theme-light .milkdown .milkdown-table-block .cell-handle .button-group button:hover {
+    background: rgba(0, 0, 0, 0.04) !important;
+    color: #1c1917 !important;
+}
+
+.milkdown .milkdown-table-block .cell-handle .button-group button:active {
+    background: rgba(0, 255, 153, 0.08) !important;
+    color: var(--accent, #00ff99) !important;
+}
+
+.theme-light .milkdown .milkdown-table-block .cell-handle .button-group button:active {
+    background: rgba(16, 185, 129, 0.06) !important;
+    color: #10b981 !important;
+}
+
+.milkdown .milkdown-table-block .cell-handle .button-group button svg {
+    color: currentColor !important;
+    fill: currentColor !important;
+    width: 14px !important;
+    height: 14px !important;
+}
+
+/* 3. Table Column/Row Insertion Lines & Add Buttons */
+.milkdown .milkdown-table-block .line-handle {
+    background-color: var(--accent) !important;
+}
+
+.theme-light .milkdown .milkdown-table-block .line-handle {
+    background-color: #10b981 !important;
+}
+
+.milkdown .milkdown-table-block .line-handle .add-button {
+    background-color: rgba(24, 24, 28, 0.85) !important;
+    backdrop-filter: blur(12px) !important;
+    -webkit-backdrop-filter: blur(12px) !important;
+    border: 1px solid rgba(255, 255, 255, 0.08) !important;
+    color: #e4e4e7 !important;
+    box-shadow: 0 4px 12px rgba(0, 0, 0, 0.3) !important;
+}
+
+.theme-light .milkdown .milkdown-table-block .line-handle .add-button {
+    background-color: rgba(254, 254, 254, 0.95) !important;
+    border: 1px solid rgba(0, 0, 0, 0.08) !important;
+    color: #57524e !important;
+    box-shadow: 0 4px 12px rgba(0, 0, 0, 0.05) !important;
+}
+
+.milkdown .milkdown-table-block .line-handle .add-button:hover {
+    background-color: rgba(255, 255, 255, 0.15) !important;
+    color: #ffffff !important;
+    border-color: var(--accent) !important;
+}
+
+.theme-light .milkdown .milkdown-table-block .line-handle .add-button:hover {
+    background-color: rgba(0, 0, 0, 0.08) !important;
+    color: #1c1917 !important;
+    border-color: #10b981 !important;
+}
+
+.milkdown .milkdown-table-block .line-handle .add-button svg {
+    width: 12px !important;
+    height: 12px !important;
+    color: currentColor !important;
+    fill: currentColor !important;
+}
+
+/* 4. Paragraph Block Drag Handles */
+.milkdown .milkdown-block-handle {
+    background-color: rgba(24, 24, 28, 0.85) !important;
+    backdrop-filter: blur(12px) !important;
+    -webkit-backdrop-filter: blur(12px) !important;
+    border: 1px solid rgba(255, 255, 255, 0.08) !important;
+    border-radius: 6px !important;
+    padding: 2px !important;
+    box-shadow: 0 4px 12px rgba(0, 0, 0, 0.3) !important;
+    display: flex; /* Removed !important to allow toggling */
+    gap: 2px !important;
+}
+
+.theme-light .milkdown .milkdown-block-handle {
+    background-color: rgba(254, 254, 254, 0.95) !important;
+    border: 1px solid rgba(0, 0, 0, 0.08) !important;
+    box-shadow: 0 4px 12px rgba(0, 0, 0, 0.05) !important;
+}
+
+.milkdown .milkdown-block-handle .operation-item {
+    border-radius: 4px !important;
+    width: 24px !important;
+    height: 24px !important;
+    padding: 4px !important;
+    display: inline-flex !important;
+    justify-content: center !important;
+    align-items: center !important;
+    color: #e4e4e7 !important;
+    transition: all 0.2s ease !important;
+}
+
+.theme-light .milkdown .milkdown-block-handle .operation-item {
+    color: #57524e !important;
+}
+
+.milkdown .milkdown-block-handle .operation-item:hover {
+    background: rgba(255, 255, 255, 0.05) !important;
+    color: #ffffff !important;
+}
+
+.theme-light .milkdown .milkdown-block-handle .operation-item:hover {
+    background: rgba(0, 0, 0, 0.04) !important;
+    color: #1c1917 !important;
+}
+
+.milkdown .milkdown-block-handle .operation-item.active {
+    background: rgba(0, 255, 153, 0.08) !important;
+    color: var(--accent, #00ff99) !important;
+}
+
+.theme-light .milkdown .milkdown-block-handle .operation-item.active {
+    background: rgba(16, 185, 129, 0.06) !important;
+    color: #10b981 !important;
+}
+
+.milkdown .milkdown-block-handle .operation-item svg {
+    width: 14px !important;
+    height: 14px !important;
+    fill: currentColor !important;
+    color: currentColor !important;
+}
+
+/* 5. Slash Commands Menu */
+.milkdown .milkdown-slash-menu {
+    background: rgba(24, 24, 28, 0.85) !important;
+    backdrop-filter: blur(12px) !important;
+    -webkit-backdrop-filter: blur(12px) !important;
+    border: 1px solid rgba(255, 255, 255, 0.08) !important;
+    border-radius: 8px !important;
+    box-shadow: 0 4px 12px rgba(0, 0, 0, 0.5), 0 12px 28px rgba(0, 0, 0, 0.4) !important;
+    font-family: var(--nexus-font-sans) !important;
+    color: #ffffff !important;
+}
+
+.theme-light .milkdown .milkdown-slash-menu {
+    background: rgba(254, 254, 254, 0.95) !important;
+    border: 1px solid rgba(0, 0, 0, 0.08) !important;
+    box-shadow: 0 4px 20px rgba(0, 0, 0, 0.05), 0 10px 30px rgba(0, 0, 0, 0.04) !important;
+    color: #2d2a26 !important;
+}
+
+.milkdown .milkdown-slash-menu .tab-group ul li {
+    color: #a1a1aa !important;
+    border-radius: 6px !important;
+    transition: all 0.2s ease !important;
+}
+
+.theme-light .milkdown .milkdown-slash-menu .tab-group ul li {
+    color: #78716c !important;
+}
+
+.milkdown .milkdown-slash-menu .tab-group ul li:hover {
+    background: rgba(255, 255, 255, 0.05) !important;
+    color: #ffffff !important;
+}
+
+.theme-light .milkdown .milkdown-slash-menu .tab-group ul li:hover {
+    background: rgba(0, 0, 0, 0.04) !important;
+    color: #1c1917 !important;
+}
+
+.milkdown .milkdown-slash-menu .tab-group ul li.selected {
+    background: rgba(0, 255, 153, 0.08) !important;
+    color: var(--accent) !important;
+}
+
+.theme-light .milkdown .milkdown-slash-menu .tab-group ul li.selected {
+    background: rgba(16, 185, 129, 0.06) !important;
+    color: #10b981 !important;
+}
+
+.milkdown .milkdown-slash-menu .menu-groups .menu-group li {
+    color: #e4e4e7 !important;
+    border-radius: 6px !important;
+    transition: all 0.2s ease !important;
+}
+
+.theme-light .milkdown .milkdown-slash-menu .menu-groups .menu-group li {
+    color: #57524e !important;
+}
+
+.milkdown .milkdown-slash-menu .menu-groups .menu-group li svg {
+    color: #a1a1aa !important;
+    fill: #a1a1aa !important;
+}
+
+.theme-light .milkdown .milkdown-slash-menu .menu-groups .menu-group li svg {
+    color: #78716c !important;
+    fill: #78716c !important;
+}
+
+.milkdown .milkdown-slash-menu .menu-groups .menu-group li.hover {
+    background: rgba(255, 255, 255, 0.05) !important;
+    color: #ffffff !important;
+}
+
+.theme-light .milkdown .milkdown-slash-menu .menu-groups .menu-group li.hover {
+    background: rgba(0, 0, 0, 0.04) !important;
+    color: #1c1917 !important;
+}
+
+.milkdown .milkdown-slash-menu .menu-groups .menu-group li.active {
+    background: rgba(0, 255, 153, 0.08) !important;
+    color: var(--accent) !important;
+}
+
+.theme-light .milkdown .milkdown-slash-menu .menu-groups .menu-group li.active {
+    background: rgba(16, 185, 129, 0.06) !important;
+    color: #10b981 !important;
+}
+
+.milkdown .milkdown-slash-menu .menu-groups .menu-group li.active svg {
+    color: var(--accent) !important;
+    fill: var(--accent) !important;
+}
+
+.theme-light .milkdown .milkdown-slash-menu .menu-groups .menu-group li.active svg {
+    color: #10b981 !important;
+    fill: #10b981 !important;
+}
+
+/* 6. Explicit Visibility State Overrides */
+.milkdown-popover[data-show="false"],
+.popover[data-show="false"],
+.prosemirror-bubble-menu[data-show="false"],
+.milkdown-toolbar[data-show="false"],
+.milkdown-slash-menu[data-show="false"],
+.milkdown-table-block .cell-handle .button-group[data-show="false"],
+.milkdown-link-preview[data-show="false"],
+.milkdown-link-edit[data-show="false"] {
+    display: none !important;
+    opacity: 0 !important;
+    visibility: hidden !important;
+    pointer-events: none !important;
+}
+
+/* 7. Table Overflow Clipping Fix for Handles */
+.milkdown .tableWrapper {
+    overflow: visible !important;
+}
+

src/NexusReader.UI.Shared/wwwroot/js/milkdownWrapper.js

@@ -0,0 +1,104 @@
+// Map to keep track of active Crepe editor instances by elementId (container ID)
+const editorCache = new Map();
+
+/**
+ * Asynchronously injects a stylesheet link tag into the document head
+ * and returns a Promise that resolves when the stylesheet is fully loaded.
+ */
+async function ensureStylesheet(href) {
+    if (document.querySelector(`link[href="${href}"]`)) {
+        return Promise.resolve();
+    }
+    return new Promise((resolve, reject) => {
+        const link = document.createElement('link');
+        link.rel = 'stylesheet';
+        link.href = href;
+        link.onload = () => resolve();
+        link.onerror = (err) => reject(new Error(`Failed to load stylesheet: ${href}. ${err}`));
+        document.head.appendChild(link);
+    });
+}
+
+/**
+ * Initializes a Milkdown Crepe editor on the specified element.
+ */
+export async function initEditor(elementId, dotNetHelper, initialMarkdown) {
+    const container = document.getElementById(elementId);
+    if (!container) {
+        console.error(`[Milkdown] Container with ID "${elementId}" not found.`);
+        return;
+    }
+
+    try {
+        // Condition 2: Prevent FOUC by loading stylesheets before instantiating the editor
+        await ensureStylesheet('/_content/NexusReader.UI.Shared/css/vendor/milkdown-crepe.css');
+
+        // Dynamically import the local JS bundle
+        await import('/_content/NexusReader.UI.Shared/js/vendor/milkdown-crepe.js');
+
+        // Get Crepe constructor from the global window.milkdownCrepe namespace
+        const Crepe = window.milkdownCrepe?.Crepe;
+        if (!Crepe) {
+            throw new Error("Crepe constructor not found on window.milkdownCrepe");
+        }
+
+        // Initialize the Crepe editor instance with custom ImageBlock upload handler
+        const crepe = new Crepe({
+            root: container,
+            defaultValue: initialMarkdown || "",
+            featureConfigs: {
+                [Crepe.Feature.ImageBlock]: {
+                    onUpload: async (file) => {
+                        try {
+                            const arrayBuffer = await file.arrayBuffer();
+                            const uint8Array = new Uint8Array(arrayBuffer);
+                            const url = await dotNetHelper.invokeMethodAsync('UploadImageFromJs', file.name, file.type, uint8Array);
+                            return url;
+                        } catch (err) {
+                            console.error("[Milkdown] Failed to upload image from JS:", err);
+                            throw err;
+                        }
+                    }
+                }
+            }
+        });
+
+        // Store the editor instance in the map
+        editorCache.set(elementId, crepe);
+
+        // Create the editor view asynchronously
+        await crepe.create();
+
+        console.log(`[Milkdown] Editor successfully initialized on element: ${elementId}`);
+    } catch (error) {
+        console.error(`[Milkdown] Failed to initialize editor on "${elementId}":`, error);
+    }
+}
+
+/**
+ * Retrieves the current Markdown content from a specific editor instance.
+ */
+export function getMarkdownContent(elementId) {
+    const crepe = editorCache.get(elementId);
+    if (!crepe) {
+        console.warn(`[Milkdown] No editor instance found for element: ${elementId}`);
+        return "";
+    }
+    return crepe.getMarkdown();
+}
+
+/**
+ * Safely disposes of the editor instance to prevent memory leaks in WASM.
+ */
+export async function destroyEditor(elementId) {
+    const crepe = editorCache.get(elementId);
+    if (crepe) {
+        try {
+            await crepe.destroy();
+            console.log(`[Milkdown] Editor instance successfully destroyed: ${elementId}`);
+        } catch (error) {
+            console.error(`[Milkdown] Error destroying editor for element "${elementId}":`, error);
+        }
+        editorCache.delete(elementId);
+    }
+}

src/NexusReader.Web/Program.cs

@@ -769,6 +769,64 @@ app.MapPost("/identity/theme", async (
     return Results.Ok();
 }).RequireAuthorization();
 
+app.MapPost("/api/media/upload", async (
+    HttpRequest request,
+    NexusReader.Application.Abstractions.Services.IStorageService storageService,
+    ILogger<Program> logger) =>
+{
+    if (!request.HasFormContentType)
+    {
+        return Results.BadRequest("Request must be a multipart form.");
+    }
+
+    var form = await request.ReadFormAsync();
+    var file = form.Files.GetFile("file");
+
+    if (file == null || file.Length == 0)
+    {
+        return Results.BadRequest("No file uploaded.");
+    }
+
+    // Size limit check (max 5MB)
+    const long maxFileSize = 5 * 1024 * 1024;
+    if (file.Length > maxFileSize)
+    {
+        return Results.BadRequest("File size exceeds the 5MB limit.");
+    }
+
+    // Read file bytes for signature check
+    byte[] fileBytes;
+    using (var memoryStream = new MemoryStream())
+    {
+        await file.CopyToAsync(memoryStream);
+        fileBytes = memoryStream.ToArray();
+    }
+
+    // Validate signature
+    if (!ValidateImageSignature(fileBytes, file.ContentType))
+    {
+        logger.LogWarning("File signature validation failed for file {FileName} with content type {ContentType}.", file.FileName, file.ContentType);
+        return Results.BadRequest("Invalid image signature. Legitimate JPEG, PNG, or WEBP images only.");
+    }
+
+    // Save using IStorageService
+    var fileUrl = await storageService.UploadFileAsync(fileBytes, file.FileName, file.ContentType);
+    return Results.Ok(new NexusReader.Application.DTOs.Media.UploadResultDto(fileUrl));
+}).DisableAntiforgery();
+
+app.MapPost("/api/chapters/validate", (
+    [Microsoft.AspNetCore.Mvc.FromBody] NexusReader.Application.DTOs.Media.ValidateChapterRequest request,
+    NexusReader.Application.Abstractions.Services.ISanitizerService sanitizerService) =>
+{
+    if (request == null || string.IsNullOrEmpty(request.Content))
+    {
+        return Results.Ok(new NexusReader.Application.DTOs.Media.ValidateChapterResponse(string.Empty));
+    }
+
+    var sanitized = sanitizerService.Sanitize(request.Content);
+    return Results.Ok(new NexusReader.Application.DTOs.Media.ValidateChapterResponse(sanitized));
+}).DisableAntiforgery();
+
 app.MapRazorComponents<App>()
     .AddInteractiveServerRenderMode()
     .AddInteractiveWebAssemblyRenderMode()
@@ -820,6 +878,34 @@ async Task TriggerBackgroundProcessingForUnindexedBooksAsync(IServiceProvider se
     }
 }
 
+static bool ValidateImageSignature(byte[] bytes, string contentType)
+{
+    if (bytes.Length < 4) return false;
+
+    // Check PNG signature: 89 50 4E 47
+    if (bytes[0] == 0x89 && bytes[1] == 0x50 && bytes[2] == 0x4E && bytes[3] == 0x47)
+    {
+        return contentType.Equals("image/png", StringComparison.OrdinalIgnoreCase);
+    }
+
+    // Check JPEG signature: FF D8 FF
+    if (bytes[0] == 0xFF && bytes[1] == 0xD8 && bytes[2] == 0xFF)
+    {
+        return contentType.Equals("image/jpeg", StringComparison.OrdinalIgnoreCase) ||
+               contentType.Equals("image/jpg", StringComparison.OrdinalIgnoreCase);
+    }
+
+    // Check WEBP signature: RIFF ... WEBP
+    if (bytes.Length >= 12 &&
+        bytes[0] == 0x52 && bytes[1] == 0x49 && bytes[2] == 0x46 && bytes[3] == 0x46 && // RIFF
+        bytes[8] == 0x57 && bytes[9] == 0x45 && bytes[10] == 0x42 && bytes[11] == 0x50) // WEBP
+    {
+        return contentType.Equals("image/webp", StringComparison.OrdinalIgnoreCase);
+    }
+
+    return false;
+}
+
 public record KnowledgeRequest(string Text, Guid? EbookId = null);
 public record GroundednessRequest(string Answer, string Context);
 public record SemanticSearchRequest(string QueryText, int Limit = 5);

tests/NexusReader.Application.Tests/Services/HtmlSanitizerServiceTests.cs

@@ -0,0 +1,54 @@
+using FluentAssertions;
+using NexusReader.Infrastructure.Services;
+using Xunit;
+
+namespace NexusReader.Application.Tests.Services;
+
+public class HtmlSanitizerServiceTests
+{
+    [Fact]
+    public void Sanitize_WithSafeInput_ReturnsSameInput()
+    {
+        // Arrange
+        var service = new HtmlSanitizerService();
+        var input = "<p>This is a safe <strong>paragraph</strong>.</p>";
+
+        // Act
+        var result = service.Sanitize(input);
+
+        // Assert
+        result.Should().Be(input);
+    }
+
+    [Fact]
+    public void Sanitize_WithScriptTag_StripsScriptTag()
+    {
+        // Arrange
+        var service = new HtmlSanitizerService();
+        var input = "<p>Hello</p><script>alert('xss')</script>";
+
+        // Act
+        var result = service.Sanitize(input);
+
+        // Assert
+        result.Should().NotContain("<script>");
+        result.Should().NotContain("alert");
+        result.Should().Be("<p>Hello</p>");
+    }
+
+    [Fact]
+    public void Sanitize_WithOnEventHandlerAttribute_StripsOnError()
+    {
+        // Arrange
+        var service = new HtmlSanitizerService();
+        var input = "<img src=\"x\" onerror=\"alert(1)\" />";
+
+        // Act
+        var result = service.Sanitize(input);
+
+        // Assert
+        result.Should().NotContain("onerror");
+        result.Should().NotContain("alert");
+        result.Should().Contain("<img src=\"x\">");
+    }
+}