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- **Cleanup**: Removed obsolete interfaces and constants that were superseded by newer Application layer implementations.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/KnowledgeCoordinator.cs

@@ -1,4 +1,5 @@
 using NexusReader.Application.Abstractions.Services;
+using FluentResults;
 using NexusReader.Application.Queries.Graph;
 using NexusReader.Application.Queries.Quiz;
 using NexusReader.UI.Shared.Services;
@@ -77,7 +78,7 @@ public sealed partial class KnowledgeCoordinator : IDisposable
         await _graphService.SetActiveNode(blockId);
     }
 
-    public async Task<KnowledgePacket?> RequestSummaryAndQuizAsync(string content, string tenantId = "global")
+    public async Task<Result<KnowledgePacket>> RequestSummaryAndQuizAsync(string content, string tenantId = "global")
     {
         await _quizService.SetHydrating(true);
         LogRequestingSummary(tenantId);
@@ -93,20 +94,21 @@ public sealed partial class KnowledgeCoordinator : IDisposable
                 
                 await _quizService.SetQuiz(null, new QuizDto(quizQuestions));
                 await _platformService.VibrateSuccessAsync();
-                return packet;
+                return Result.Ok(packet);
             }
 
             LogSummaryWarning(tenantId);
+            return Result.Fail(result.Errors);
         }
         catch (Exception ex)
         {
             LogSummaryError(ex, tenantId);
+            return Result.Fail(new Error("Error requesting summary and quiz").CausedBy(ex));
         }
         finally
         {
             await _quizService.SetHydrating(false);
         }
-        return null;
     }
 
     public async Task ClearAsync()