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.UI.Shared/Services/IReaderNavigationService.cs

@@ -2,19 +2,20 @@ namespace NexusReader.UI.Shared.Services;
 
 public interface IReaderNavigationService
 {
+    Guid CurrentEbookId { get; }
     int CurrentChapterIndex { get; }
     int TotalChapters { get; }
     string ChapterTitle { get; }
-    
+
     event Func<Task>? OnNavigationChanged;
-    
+
     Task GoToChapter(int index);
     Task GoToNextChapter();
     Task GoToPreviousChapter();
     Task UpdateMetadataAsync(int currentIndex, int totalChapters, string title);
-    
+
     /// <summary>
-    /// Navigates to the reader for a specific book.
+    /// Navigates to the reader for a specific book and records the current ebook ID.
     /// </summary>
     void NavigateToBook(Guid bookId);
 }