style: complete Light Sepia theme overrides for user dashboard (#78)

Resolves #79

This Pull Request completes the visual implementation of the premium **"Warm Paper / Soft Sepia"** light theme across all user dashboard sub-modules and components.

### 🎨 Styling Refactoring & Light Sepia Layout
We refactored isolated component styles (`.razor.css`) to ensure proper contrast, remove hardcoded dark tokens, and fix text visibility under the `.theme-light` environment:

1. **Dashboard & Sidebar Layouts:**
   * **MainHubLayout.razor.css** & **Dashboard.razor.css**: Replaced hardcoded dark backgrounds with `var(--bg-surface)` and `var(--bg-base)`. Overrode user name brackets, progress bar elements, active quiz cards, graph nodes, and buttons.
2. **Catalog & Library Pages:**
   * **Catalog.razor.css** & **MyBooks.razor.css**: Adjusted cover hover actions, overlay transparency, and progress tracks. Fixed course tile background gradients to use a warm, elegant `#e4e1d9` layer and `var(--text-main)` code text.
3. **Profile & Settings Views:**
   * **Profile.razor.css** & **Settings.razor.css**: Overrode token usage progress tracks, page title gradient transparency, section descriptions, and diagnostic button styling.
4. **Concepts Dashboard & Interactive Widgets:**
   * **ConceptsDashboard.razor.css** & **ConceptsMap.razor.css**: Transitioned node headers, unlocked/locked badges, warning blocks, and term pills to semantic colors. Removed neon glow animations for locked nodes.
5. **Intelligence Workspace & AI Responses:**
   * **Intelligence.razor.css** & **AiResponseRenderer.razor.css**: Refactored empty state welcome messages, placeholder styles, input fields, and robot avatar borders. Refined the linear-gradient mask fade effect to blend correctly into the light sepia surface environment rather than dropping into dark transparent channels.
6. **Dashboard Sidebar Widgets:**
   * **CurrentReadingWidget.razor.css** & **ContextualRecommendationsWidget.razor.css**: Replaced hardcoded `#1a1a1e` card containers and light text colors with semantic variables (`var(--bg-surface)`, `var(--border)`, `var(--text-main)`, and `var(--text-muted)`).

### 🛠️ Blazor CSS Isolation Compiler Compliance
* Avoided the use of `:global(.theme-light)` selector overrides within isolated CSS rules because they are unsupported by Blazor's CSS isolation compiler and cause the compiled stylesheet to ignore them.
* Replaced them with the correct standard selector format `.theme-light .some-class` which properly compiles to `.theme-light .some-class[b-xxxx]`, applying correct theme styles recursively to child scoped markup.

### 🧪 Verification
* Checked that the solution builds cleanly with 0 compiler errors: `dotnet build NexusReader.slnx --no-restore`
* Ran all unit tests successfully: `dotnet test NexusReader.slnx --no-restore`

---------

Co-authored-by: Marek Jasiński <jasins.marek@gmail.com>
Reviewed-on: #78
Co-authored-by: Antigravity <antigravity@google.com>
Co-committed-by: Antigravity <antigravity@google.com>

src/NexusReader.Web/Components/App.razor

@@ -11,13 +11,28 @@
 
     <script>
         (function () {
-            const savedTheme = localStorage.getItem('theme');
-            const systemPrefersDark = window.matchMedia('(prefers-color-scheme: dark)').matches;
-            const isLight = savedTheme === 'light' || (!savedTheme && !systemPrefersDark);
-            if (isLight) {
-                document.documentElement.classList.add('theme-light');
-            } else {
-                document.documentElement.classList.remove('theme-light');
+            try {
+                var themeMode = localStorage.getItem('theme-mode');
+                var savedTheme = localStorage.getItem('theme');
+                var isLight = false;
+                
+                if (themeMode === '2' || savedTheme === 'light') {
+                    isLight = true;
+                } else if (themeMode === '1' || savedTheme === 'dark') {
+                    isLight = false;
+                } else {
+                    isLight = window.matchMedia && window.matchMedia('(prefers-color-scheme: light)').matches;
+                }
+                
+                if (isLight) {
+                    document.documentElement.classList.add('theme-light');
+                    document.documentElement.classList.remove('theme-dark');
+                } else {
+                    document.documentElement.classList.add('theme-dark');
+                    document.documentElement.classList.remove('theme-light');
+                }
+            } catch (e) {
+                // Fail silently
             }
         })();
     </script>

src/NexusReader.Web/Program.cs

@@ -52,7 +52,9 @@ builder.Services.AddHttpContextAccessor();
 
 builder.Services.AddScoped<IPlatformService, WebPlatformService>();
 builder.Services.AddScoped<INativeStorageService, NexusReader.Web.Services.NativeStorageService>();
-builder.Services.AddScoped<IThemeService, ThemeService>();
+builder.Services.AddScoped<IUserPreferenceStore, NexusReader.Web.Services.ServerUserPreferenceStore>();
+builder.Services.AddScoped<IThemeService, NexusReader.Web.Services.ServerThemeService>();
+builder.Services.AddScoped<IRecommendationService, NexusReader.Web.Services.ServerRecommendationService>();
 // Feature settings (avoiding direct raw IConfiguration injection in client pages)
 var featureSettings = builder.Configuration.GetSection("Features").Get<FeatureSettings>() ?? new FeatureSettings();
 builder.Services.AddSingleton(featureSettings);
@@ -753,6 +755,20 @@ app.MapGet("/identity/profile", async (ClaimsPrincipal user, IMediator mediator)
     return Results.Ok(result.Value);
 }).RequireAuthorization();
 
+app.MapPost("/identity/theme", async (
+    [Microsoft.AspNetCore.Mvc.FromBody] NexusReader.Application.DTOs.User.UpdateThemeRequest request,
+    ClaimsPrincipal user,
+    IMediator mediator) =>
+{
+    var userId = user.FindFirstValue(ClaimTypes.NameIdentifier);
+    if (string.IsNullOrEmpty(userId)) return Results.Unauthorized();
+
+    var result = await mediator.Send(new NexusReader.Application.Commands.User.UpdateThemeCommand(userId, request.Mode));
+    if (result.IsFailed) return Results.BadRequest(result.Errors.FirstOrDefault()?.Message);
+
+    return Results.Ok();
+}).RequireAuthorization();
+
 app.MapRazorComponents<App>()
     .AddInteractiveServerRenderMode()
     .AddInteractiveWebAssemblyRenderMode()

src/NexusReader.Web/Services/ServerRecommendationService.cs

@@ -0,0 +1,50 @@
+using System.Collections.Generic;
+using System.Security.Claims;
+using System.Threading;
+using System.Threading.Tasks;
+using FluentResults;
+using MediatR;
+using Microsoft.AspNetCore.Http;
+using NexusReader.Application.Queries.Recommendations;
+using NexusReader.UI.Shared.Services;
+
+namespace NexusReader.Web.Services;
+
+/// <summary>
+/// Server-side implementation of <see cref="IRecommendationService"/> that executes
+/// the MediatR query directly inside the Web Server's request context.
+/// </summary>
+public sealed class ServerRecommendationService : IRecommendationService
+{
+    private readonly IMediator _mediator;
+    private readonly IHttpContextAccessor _httpContextAccessor;
+
+    public ServerRecommendationService(IMediator mediator, IHttpContextAccessor httpContextAccessor)
+    {
+        _mediator = mediator;
+        _httpContextAccessor = httpContextAccessor;
+    }
+
+    public async Task<List<RecommendationDto>?> GetRecommendationsAsync(CancellationToken cancellationToken = default)
+    {
+        var httpContext = _httpContextAccessor.HttpContext;
+        if (httpContext?.User == null)
+        {
+            return new List<RecommendationDto>();
+        }
+
+        var userId = httpContext.User.FindFirstValue(ClaimTypes.NameIdentifier);
+        if (string.IsNullOrEmpty(userId))
+        {
+            return new List<RecommendationDto>();
+        }
+
+        var result = await _mediator.Send(new GetContextualRecommendationsQuery(userId), cancellationToken);
+        if (result.IsSuccess && result.Value != null)
+        {
+            return result.Value.Recommendations;
+        }
+
+        return new List<RecommendationDto>();
+    }
+}

src/NexusReader.Web/Services/ServerThemeService.cs

@@ -0,0 +1,21 @@
+using NexusReader.Domain.Enums;
+using NexusReader.UI.Shared.Services;
+
+namespace NexusReader.Web.Services;
+
+public sealed class ServerThemeService : IThemeService
+{
+    public ThemeMode Mode => ThemeMode.System;
+    public bool IsLightMode => false;
+
+    // Explicit event implementation to avoid CS0067 warning about unused events on the server
+    public event Action<ThemeMode>? OnThemeChanged
+    {
+        add { }
+        remove { }
+    }
+
+    public Task InitializeAsync() => Task.CompletedTask;
+    public Task SetThemeAsync(ThemeMode mode) => Task.CompletedTask;
+    public Task ToggleTheme() => Task.CompletedTask;
+}

src/NexusReader.Web/Services/ServerUserPreferenceStore.cs

@@ -0,0 +1,78 @@
+using System.Security.Claims;
+using FluentResults;
+using Microsoft.AspNetCore.Http;
+using Microsoft.EntityFrameworkCore;
+using NexusReader.Data.Persistence;
+using NexusReader.Domain.Enums;
+using NexusReader.Application.Abstractions.Services;
+
+namespace NexusReader.Web.Services;
+
+public class ServerUserPreferenceStore : IUserPreferenceStore
+{
+    private readonly IDbContextFactory<AppDbContext> _dbContextFactory;
+    private readonly IHttpContextAccessor _httpContextAccessor;
+
+    public ServerUserPreferenceStore(
+        IDbContextFactory<AppDbContext> dbContextFactory,
+        IHttpContextAccessor httpContextAccessor)
+    {
+        _dbContextFactory = dbContextFactory;
+        _httpContextAccessor = httpContextAccessor;
+    }
+
+    public async Task<Result> SaveThemePreferenceAsync(ThemeMode mode)
+    {
+        var userId = _httpContextAccessor.HttpContext?.User.FindFirstValue(ClaimTypes.NameIdentifier);
+        if (string.IsNullOrEmpty(userId))
+        {
+            return Result.Fail("User is not authenticated on the server.");
+        }
+
+        try
+        {
+            using var dbContext = await _dbContextFactory.CreateDbContextAsync();
+            var user = await dbContext.Users
+                .AsTracking()
+                .FirstOrDefaultAsync(u => u.Id == userId);
+                
+            if (user == null)
+            {
+                return Result.Fail("User not found in database.");
+            }
+
+            user.ThemePreference = mode;
+            await dbContext.SaveChangesAsync();
+            return Result.Ok();
+        }
+        catch (Exception ex)
+        {
+            return Result.Fail(new Error("Database failure updating theme preference.").CausedBy(ex));
+        }
+    }
+
+    public async Task<Result<ThemeMode>> GetThemePreferenceAsync()
+    {
+        var userId = _httpContextAccessor.HttpContext?.User.FindFirstValue(ClaimTypes.NameIdentifier);
+        if (string.IsNullOrEmpty(userId))
+        {
+            return Result.Fail("User is not authenticated on the server.");
+        }
+
+        try
+        {
+            using var dbContext = await _dbContextFactory.CreateDbContextAsync();
+            var user = await dbContext.Users.FirstOrDefaultAsync(u => u.Id == userId);
+            if (user == null)
+            {
+                return Result.Fail("User not found in database.");
+            }
+
+            return Result.Ok(user.ThemePreference);
+        }
+        catch (Exception ex)
+        {
+            return Result.Fail(new Error("Database failure reading theme preference.").CausedBy(ex));
+        }
+    }
+}