feat: Ingestion Pipeline Stabilization and WASM Service Proxies (#42)

This PR stabilizes the Nexus Ingestion Engine by implementing functional service proxies for the Blazor WASM client and refining the backend infrastructure for real-time progress tracking and database compatibility.

### Key Changes
- **Infrastructure Stabilization**:
  - Implemented production-grade `EbookRepository` with PostgreSQL `EF.Functions.ILike` support.
  - Enforced `IsReadyForReading = false` state for newly added ebooks (resolves #35).
  - Updated `SignalRSyncBroadcaster` to support targeted user messaging and ingestion-specific progress updates (resolves #37).
- **WASM Client Functional Proxies**:
  - Replaced "Throwing" dummy services with `WasmEbookRepository`, `WasmSyncBroadcaster`, `WasmBookStorageService`, and `WasmEmbeddingGenerator`.
  - These services proxy requests to the backend via a new set of Minimal API endpoints in `NexusReader.Web`.
- **Domain Refinement**:
  - Added `IsReadyForReading` flag to the `Ebook` entity to manage background AI processing states.

### Related Issues
- Fixes #35
- Fixes #36
- Fixes #37

---------

Co-authored-by: Marek Jasiński <jasins.marek@gmail.com>
Reviewed-on: #42
Co-authored-by: Antigravity <antigravity@google.com>
Co-committed-by: Antigravity <antigravity@google.com>

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

@@ -1,30 +1,27 @@
 using FluentResults;
 using MediatR;
-using Microsoft.EntityFrameworkCore;
 using NexusReader.Application.Abstractions.Messaging;
+using NexusReader.Application.Abstractions.Persistence;
 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 IEbookRepository _ebookRepository;
     private readonly IBookStorageService _storageService;
 
     public IngestEbookCommandHandler(
-        IDbContextFactory<AppDbContext> dbContextFactory,
+        IEbookRepository ebookRepository,
         IBookStorageService storageService)
     {
-        _dbContextFactory = dbContextFactory;
+        _ebookRepository = ebookRepository;
         _storageService = storageService;
     }
 
     public async Task<Result<Guid>> Handle(IngestEbookCommand request, CancellationToken cancellationToken)
     {
-        using var context = await _dbContextFactory.CreateDbContextAsync(cancellationToken);
-        
         string epubPath;
         string? coverUrl;
 
@@ -36,6 +33,10 @@ public class IngestEbookCommandHandler : IRequestHandler<IngestEbookCommand, Res
                 ? await _storageService.SaveCoverAsync(request.CoverImage, $"{request.Title}_cover.jpg")
                 : null;
         }
+        catch (IOException ex)
+        {
+            return Result.Fail(new Error($"Storage I/O failure: {ex.Message}").CausedBy(ex));
+        }
         catch (Exception ex)
         {
             return Result.Fail(new Error($"Storage failure: {ex.Message}").CausedBy(ex));
@@ -43,17 +44,16 @@ public class IngestEbookCommandHandler : IRequestHandler<IngestEbookCommand, Res
 
         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);
+            // 2. Resolve Author (case-insensitive via repository)
+            var authorName = string.IsNullOrWhiteSpace(request.AuthorName)
+                ? "Unknown Author"
+                : request.AuthorName.Trim();
 
+            var author = await _ebookRepository.FindAuthorByNameAsync(authorName, cancellationToken);
             if (author == null)
             {
                 author = new Author { Name = authorName };
-                context.Authors.Add(author);
+                _ebookRepository.AddAuthor(author);
             }
 
             // 3. Create Ebook
@@ -61,25 +61,21 @@ public class IngestEbookCommandHandler : IRequestHandler<IngestEbookCommand, Res
             {
                 Title = request.Title,
                 Author = author,
-                FilePath = epubPath, // Relative URL from wwwroot
+                FilePath = epubPath,
                 CoverUrl = coverUrl,
                 UserId = request.UserId,
                 TenantId = request.TenantId,
                 AddedDate = DateTime.UtcNow
             };
 
-            context.Ebooks.Add(ebook);
-            await context.SaveChangesAsync(cancellationToken);
+            _ebookRepository.AddEbook(ebook);
+            await _ebookRepository.SaveChangesAsync(cancellationToken);
 
             return Result.Ok(ebook.Id);
         }
-        catch (DbUpdateException ex)
+        catch (Exception 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));
-        }
     }
 }