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- **Cleanup**: Removed obsolete interfaces and constants that were superseded by newer Application layer implementations.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.Web/appsettings.json

@@ -0,0 +1,35 @@
+{
+  "Stripe": {
+    "ApiKey": "sk_test_placeholder",
+    "WebhookSecret": "whsec_placeholder",
+    "ProProductId": "prod_Pro123",
+    "BasicProductId": "prod_Basic456",
+    "FreeProductId": "prod_Free789"
+  },
+  "Logging": {
+    "LogLevel": {
+      "Default": "Information",
+      "Microsoft.AspNetCore": "Warning"
+    }
+  },
+  "AllowedHosts": "*",
+  "ConnectionStrings": {
+    "SqliteConnection": "Data Source=nexus.db",
+    "PostgresConnection": "Host=localhost;Database=nexus_db;Username=nexus_user;Password=nexus_password"
+  },
+  "Authentication": {
+    "Google": {
+      "ClientId": "YOUR_CLIENT_ID.apps.googleusercontent.com",
+      "ClientSecret": "YOUR_CLIENT_SECRET"
+    }
+  },
+  "Ai": {
+    "Google": {
+      "ApiKey": "PLACEHOLDER",
+      "Model": "gemini-2.5-flash-lite",
+      "MaxInputTokens": 15000,
+      "MaxOutputTokens": 8192
+    }
+  },
+  "ApiBaseUrl": "http://localhost:5000"
+}