refactor(arch): introduce IEbookRepository, ISyncBroadcaster, fix EpubReader path resolution

Critical fixes (review findings #1, #2, #3):
- Create IEbookRepository abstraction in Application layer
- Remove illegal EF Core dependency from IngestEbookCommandHandler
- Create EbookRepository implementation in Infrastructure/Persistence
- Create ISyncBroadcaster in Application/Abstractions/Messaging
- Create SignalRSyncBroadcaster in Infrastructure/RealTime
- Move UpdateReadingProgressCommandHandler from Infrastructure → Application
- Add EbookId to GetReaderPageQuery and IEpubReader signature
- Rewrite EpubReaderService: DB-resolved file path, remove auto-provisioning
- Split EpubService.cs into EpubReaderService.cs + EpubMetadataExtractor.cs
- Add CurrentEbookId to IReaderNavigationService and ReaderNavigationService
- Update WasmEpubReader and /api/epub endpoint for new signature

High severity fixes (#4, #6, #7, #8, #16):
- Change BookStorageService registration from Singleton → Scoped
- Fix empty catch{} in ReaderCanvas JS interop init — now logs warnings
- Replace all Console.WriteLine with ILogger in KnowledgeService + ReaderCanvas
- Cache JsonSerializerOptions as static field in KnowledgeService
- Wrap SyncService Task.Run body in comprehensive try/catch with ILogger

Medium/Low fixes (#11, #13, #14, #15, #18, #20):
- BookIngestionModal.DisposeAsync now nullifies _epubBytes (50MB array)
- KnowledgeCoordinator.OnGraphUpdated: Action<T> → Func<T, Task>
- BookStorageService: Path.Combine → forward-slash string interpolation
- SignalR CancellationToken passed as named parameter (not payload arg)

src/NexusReader.UI.Shared/Services/ReaderNavigationService.cs

@@ -1,4 +1,3 @@
-using System.Linq;
 using Microsoft.AspNetCore.Components;
 
 namespace NexusReader.UI.Shared.Services;
@@ -12,6 +11,7 @@ public class ReaderNavigationService : IReaderNavigationService
         _navigationManager = navigationManager;
     }
 
+    public Guid CurrentEbookId { get; private set; } = Guid.Empty;
     public int CurrentChapterIndex { get; private set; } = 0;
     public int TotalChapters { get; private set; } = 1;
     public string ChapterTitle { get; private set; } = "Loading...";
@@ -21,7 +21,7 @@ public class ReaderNavigationService : IReaderNavigationService
     public async Task GoToChapter(int index)
     {
         if (index < 0 || index >= TotalChapters) return;
-        
+
         CurrentChapterIndex = index;
         await NotifyNavigationChangedAsync();
     }
@@ -48,7 +48,7 @@ public class ReaderNavigationService : IReaderNavigationService
         if (CurrentChapterIndex != currentIndex) { CurrentChapterIndex = currentIndex; changed = true; }
         if (TotalChapters != totalChapters) { TotalChapters = totalChapters; changed = true; }
         if (ChapterTitle != title) { ChapterTitle = title; changed = true; }
-        
+
         if (changed)
         {
             await NotifyNavigationChangedAsync();
@@ -57,6 +57,8 @@ public class ReaderNavigationService : IReaderNavigationService
 
     public void NavigateToBook(Guid bookId)
     {
+        CurrentEbookId = bookId;
+        CurrentChapterIndex = 0;
         _navigationManager.NavigateTo($"/reader/{bookId}");
     }