Refactor: Web Consolidation and Identity Stabilization (#40)

## Overview
This PR completes the architectural consolidation of the web project and stabilizes the Identity-based authentication flow for the NexusReader application. It also refines the UI aesthetic for the Book Ingestion Modal as requested in #33.

## Key Changes
- **Project Consolidation**: Fully merged `NexusReader.Web.New` into `NexusReader.Web`. This includes updating all namespace references, VS Code launch/task configurations, and CI/CD (`Dockerfile`).
- **Identity Stabilization**:
  - Implemented `IIdentityService` on the server using `SignInManager<NexusUser>` and `UserManager<NexusUser>`.
  - Fixed registration logic to include mandatory fields (`SubscriptionPlanId`, `TenantId`).
  - Updated `Login.razor` to force a page reload on successful login, ensuring proper synchronization of authentication cookies between SignalR and the browser.
- **UI/UX Refinement**:
  - Updated `BookIngestionModal` styling to follow the **Nexus Neon** design system.
  - Added premium button styles with hover effects and glows.
  - Improved modal layout and interaction feedback (shimmer effects, spinner colors).
- **Cleanup**: Removed obsolete interfaces and constants that were superseded by newer Application layer implementations.

## Verification
- Successfully built the solution: `dotnet build NexusReader.slnx --no-restore`
- Verified project structure and file moves.
- Validated server-side authentication logic.

Fixes #33

---------

Co-authored-by: Marek Jasiński <jasins.marek@gmail.com>
Reviewed-on: #40
Co-authored-by: Antigravity <antigravity@google.com>
Co-committed-by: Antigravity <antigravity@google.com>

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

@@ -34,7 +34,7 @@ public class ReaderNavigationService : IReaderNavigationService
         }
     }
 
-    public void UpdateMetadata(int currentIndex, int totalChapters, string title)
+    public async Task UpdateMetadataAsync(int currentIndex, int totalChapters, string title)
     {
         bool changed = false;
         if (CurrentChapterIndex != currentIndex) { CurrentChapterIndex = currentIndex; changed = true; }
@@ -43,9 +43,7 @@ public class ReaderNavigationService : IReaderNavigationService
         
         if (changed)
         {
-            // Note: UpdateMetadata remains void, so we trigger notification fire-and-forget here
-            // but usually this is called during a render cycle where metadata is updated from a load.
-            _ = NotifyNavigationChangedAsync();
+            await NotifyNavigationChangedAsync();
         }
     }