feat(ingestion): implement hybrid metadata verification form #34 (#41)

### Description
This PR implements **Issue #34: [UI/UX] Implement Hybrid Metadata Verification Form in Ingestion Modal**.

### Key Changes
- **Metadata Verification State**: Introduced a new state in `BookIngestionModal.razor` allowing users to edit `Title` and `Author` before final ingestion.
- **Cover Image Preview**: Added a high-fidelity cover preview with a CSS-based glowing placeholder fallback for books without embedded covers.
- **Ingestion Pipeline**:
  - Implemented `IngestEbookCommand` and `IngestEbookCommandHandler`.
  - Added `IBookStorageService` and its implementation for managing EPUB and cover file storage.
  - Exposed `POST /api/library/ingest` Minimal API endpoint with `.DisableAntiforgery()` to handle client-side JSON uploads.
- **Stability Fixes**:
  - Resolved DI validation errors in the WASM client by providing a dummy `IBookStorageService` registration.
  - Adjusted Kestrel request limits to handle large EPUB payloads (up to 100MB).
  - Corrected middleware ordering to ensure Antiforgery works correctly with Authentication.

### Verification
- Solution builds successfully.
- Manual verification of modal state transitions and API ingestion logic.

Closes #34.

---------

Co-authored-by: Marek Jasiński <jasins.marek@gmail.com>
Reviewed-on: #41
Reviewed-by: Marek Jaisński <jasins.marek@gmail.com>
Co-authored-by: Antigravity <antigravity@google.com>
Co-committed-by: Antigravity <antigravity@google.com>

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

@@ -0,0 +1,29 @@
+namespace NexusReader.Application.Abstractions.Services;
+
+/// <summary>
+/// Service for managing ebook and cover file storage.
+/// </summary>
+public interface IBookStorageService
+{
+    /// <summary>
+    /// Saves an ebook file and returns its relative path/URL.
+    /// </summary>
+    Task<string> SaveEbookAsync(byte[] data, string fileName);
+
+    /// <summary>
+    /// Saves an ebook file using a stream and returns its relative path/URL.
+    /// </summary>
+    Task<string> SaveEbookAsync(Stream data, string fileName);
+
+    /// <summary>
+    /// Saves a cover image and returns its relative path/URL. 
+    /// Returns null if no cover data is provided.
+    /// </summary>
+    Task<string?> SaveCoverAsync(byte[] data, string fileName);
+
+    /// <summary>
+    /// Saves a cover image using a stream and returns its relative path/URL.
+    /// Returns null if no cover data is provided.
+    /// </summary>
+    Task<string?> SaveCoverAsync(Stream data, string fileName);
+}

src/NexusReader.Application/Commands/Library/IngestEbookCommand.cs

@@ -0,0 +1,21 @@
+using NexusReader.Application.Abstractions.Messaging;
+
+namespace NexusReader.Application.Commands.Library;
+
+/// <summary>
+/// Command to ingest a new ebook into the library.
+/// </summary>
+/// <param name="Title">The title of the book.</param>
+/// <param name="AuthorName">The name of the author.</param>
+/// <param name="CoverImage">The raw bytes of the cover image (optional).</param>
+/// <param name="EpubData">The raw bytes of the EPUB file.</param>
+/// <param name="UserId">The ID of the user owning the book.</param>
+/// <param name="TenantId">The tenant ID for multi-tenant isolation. Defaults to "global" for single-tenant or default usage.</param>
+public record IngestEbookCommand(
+    string Title,
+    string AuthorName,
+    byte[]? CoverImage,
+    byte[] EpubData,
+    string UserId,
+    string TenantId = "global"
+) : ICommand<Guid>;

src/NexusReader.Application/Commands/Library/IngestEbookCommandHandler.cs

@@ -0,0 +1,85 @@
+using FluentResults;
+using MediatR;
+using Microsoft.EntityFrameworkCore;
+using NexusReader.Application.Abstractions.Messaging;
+using NexusReader.Application.Abstractions.Services;
+using NexusReader.Data.Persistence;
+using NexusReader.Domain.Entities;
+
+namespace NexusReader.Application.Commands.Library;
+
+public class IngestEbookCommandHandler : IRequestHandler<IngestEbookCommand, Result<Guid>>
+{
+    private readonly IDbContextFactory<AppDbContext> _dbContextFactory;
+    private readonly IBookStorageService _storageService;
+
+    public IngestEbookCommandHandler(
+        IDbContextFactory<AppDbContext> dbContextFactory,
+        IBookStorageService storageService)
+    {
+        _dbContextFactory = dbContextFactory;
+        _storageService = storageService;
+    }
+
+    public async Task<Result<Guid>> Handle(IngestEbookCommand request, CancellationToken cancellationToken)
+    {
+        using var context = await _dbContextFactory.CreateDbContextAsync(cancellationToken);
+        
+        string epubPath;
+        string? coverUrl;
+
+        try
+        {
+            // 1. Save Files
+            epubPath = await _storageService.SaveEbookAsync(request.EpubData, $"{request.Title}.epub");
+            coverUrl = request.CoverImage != null && request.CoverImage.Length > 0
+                ? await _storageService.SaveCoverAsync(request.CoverImage, $"{request.Title}_cover.jpg")
+                : null;
+        }
+        catch (Exception ex)
+        {
+            return Result.Fail(new Error($"Storage failure: {ex.Message}").CausedBy(ex));
+        }
+
+        try
+        {
+            // 2. Resolve Author
+            var authorName = string.IsNullOrWhiteSpace(request.AuthorName) ? "Unknown Author" : request.AuthorName.Trim();
+            
+            // Use case-insensitive comparison
+            var author = await context.Authors
+                .FirstOrDefaultAsync(a => a.Name.ToLower() == authorName.ToLower(), cancellationToken);
+
+            if (author == null)
+            {
+                author = new Author { Name = authorName };
+                context.Authors.Add(author);
+            }
+
+            // 3. Create Ebook
+            var ebook = new Ebook
+            {
+                Title = request.Title,
+                Author = author,
+                FilePath = epubPath, // Relative URL from wwwroot
+                CoverUrl = coverUrl,
+                UserId = request.UserId,
+                TenantId = request.TenantId,
+                AddedDate = DateTime.UtcNow
+            };
+
+            context.Ebooks.Add(ebook);
+            await context.SaveChangesAsync(cancellationToken);
+
+            return Result.Ok(ebook.Id);
+        }
+        catch (DbUpdateException ex)
+        {
+            return Result.Fail(new Error($"Database error during ingestion: {ex.Message}").CausedBy(ex));
+        }
+        catch (Exception ex)
+        {
+            return Result.Fail(new Error($"Unexpected error during ingestion: {ex.Message}").CausedBy(ex));
+        }
+    }
+}

src/NexusReader.Application/Commands/Library/IngestEbookRequest.cs

@@ -0,0 +1,8 @@
+namespace NexusReader.Application.Commands.Library;
+
+public record IngestEbookRequest(
+    string Title,
+    string AuthorName,
+    string? CoverImageBase64,
+    string EpubDataBase64
+);

src/NexusReader.Application/Queries/Reader/LocalEpubMetadata.cs

@@ -1,7 +1,22 @@
 namespace NexusReader.Application.Queries.Reader;
 
-public record LocalEpubMetadata(
-    string Title, 
-    string Author, 
-    byte[]? CoverImage = null
-);
+/// <summary>
+/// Represents metadata extracted from a local EPUB file.
+/// </summary>
+public record LocalEpubMetadata
+{
+    /// <summary>
+    /// The title of the book.
+    /// </summary>
+    public string Title { get; set; } = string.Empty;
+
+    /// <summary>
+    /// The author(s) of the book.
+    /// </summary>
+    public string Author { get; set; } = string.Empty;
+
+    /// <summary>
+    /// The raw bytes of the cover image, if available.
+    /// </summary>
+    public byte[]? CoverImage { get; set; }
+}