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- **Cleanup**: Removed obsolete interfaces and constants that were superseded by newer Application layer implementations.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/Pages/Account/Login.razor

@@ -6,6 +6,7 @@
 @using NexusReader.UI.Shared.Components.Atoms
 @inject IIdentityService IdentityService
 @inject NavigationManager NavigationManager
+@inject IJSRuntime JS
 
 <div class="login-page-container">
     <div class="mesh-bg"></div>
@@ -90,6 +91,12 @@
     </div>
 </div>
 
+<form id="nexusLoginForm" method="post" action="/account/login-form" style="display:none">
+    <input type="hidden" name="email" value="@_loginModel.Email" />
+    <input type="hidden" name="password" value="@_loginModel.Password" />
+    <input type="hidden" name="rememberMe" value="@(_loginModel.RememberMe ? "true" : "false")" />
+</form>
+
 @code {
     [Parameter]
     [SupplyParameterFromQuery(Name = "error")]
@@ -125,7 +132,8 @@
             var result = await IdentityService.LoginAsync(_loginModel.Email, _loginModel.Password, _loginModel.RememberMe);
             if (result.IsSuccess) 
             {
-                NavigationManager.NavigateTo("/");
+                // Trigger hidden form submission to perform cookie-based sign-in
+                await JS.InvokeVoidAsync("eval", "document.getElementById('nexusLoginForm').submit()");
             }
             else 
             {