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- **Cleanup**: Removed obsolete interfaces and constants that were superseded by newer Application layer implementations.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

@@ -1,9 +1,10 @@
 using NexusReader.Domain.Entities;
+using FluentResults;
 
 namespace NexusReader.Application.Abstractions.Services;
 
 public interface IBillingService
 {
-    Task<bool> HandleSubscriptionUpdatedAsync(string customerEmail, string stripeProductId);
-    Task<bool> HandleSubscriptionDeletedAsync(string customerEmail);
+    Task<Result> HandleSubscriptionUpdatedAsync(string customerEmail, string stripeProductId);
+    Task<Result> HandleSubscriptionDeletedAsync(string customerEmail);
 }

src/NexusReader.Application/Abstractions/Services/IEpubMetadataExtractor.cs

@@ -0,0 +1,10 @@
+using FluentResults;
+using NexusReader.Application.Queries.Reader;
+using System.IO;
+
+namespace NexusReader.Application.Abstractions.Services;
+
+public interface IEpubMetadataExtractor
+{
+    Task<Result<LocalEpubMetadata>> ExtractMetadataAsync(Stream epubStream);
+}

src/NexusReader.Application/Abstractions/Services/IEpubReader.cs

@@ -3,7 +3,7 @@ using NexusReader.Application.Queries.Reader;
 
 namespace NexusReader.Application.Abstractions.Services;
 
-public interface IEpubService
+public interface IEpubReader
 {
     Task<Result<ReaderPageViewModel>> GetEpubContentAsync(int chapterIndex, string? userId = null);
 }

src/NexusReader.Application/Abstractions/Services/IIdentityService.cs

@@ -0,0 +1,14 @@
+using FluentResults;
+using NexusReader.Application.DTOs.User;
+
+namespace NexusReader.Application.Abstractions.Services;
+
+public interface IIdentityService
+{
+    event Func<Task>? OnStateInvalidated;
+    Task<Result> RegisterAsync(string email, string password);
+    Task<Result> LoginAsync(string email, string password, bool rememberMe = false);
+    Task<Result> LogoutAsync();
+    Task<Result<UserProfileDto>> GetProfileAsync();
+    Task<Result> RefreshTokenAsync();
+}

src/NexusReader.Application/Abstractions/Services/INativeStorageService.cs

@@ -4,13 +4,13 @@ namespace NexusReader.Application.Abstractions.Services;
 
 public interface INativeStorageService
 {
-    Result SaveString(string key, string value);
-    Result<string?> GetString(string key);
-    Result SaveBool(string key, bool value);
-    Result<bool> GetBool(string key, bool defaultValue = false);
-    Result Remove(string key);
+    Task<Result> SaveStringAsync(string key, string value);
+    Task<Result<string?>> GetStringAsync(string key);
+    Task<Result> SaveBoolAsync(string key, bool value);
+    Task<Result<bool>> GetBoolAsync(string key, bool defaultValue = false);
+    Task<Result> RemoveAsync(string key);
     
     Task<Result> SaveSecureString(string key, string value);
     Task<Result<string?>> GetSecureString(string key);
-    Result RemoveSecure(string key);
+    Task<Result> RemoveSecureAsync(string key);
 }