feat(infra): Docker-compose configuration and environment-specific security guards for Beta deployment to Test environment (#56)

This pull request introduces the dedicated containerized infrastructure and configuration for deploying NexusReader's beta version in the Test environment.

### Summary of Changes

1. **Docker Infrastructure & Secrets**:
   - **`docker-compose.test.yml`**: Configured dedicated database and auxiliary services (PostgreSQL 17, Qdrant, Neo4j) on isolated, non-standard ports to ensure zero conflict with the existing server configurations.
   - **`.env.test.template`**: Provided an environment variable template showing required setups, including mandatory database passwords, API keys, and admin custom passwords.
   - **`.gitignore`**: Excluded local `.env` files to prevent accidental commits of production or staging secrets.

2. **Database Hardening**:
   - Configured Neo4j with basic authentication (`IDriver` instantiation uses basic auth when credentials are provided in configuration).
   - Configured PostgreSQL to use mandatory authentication.
   - Configured the admin seeder (`DbInitializer.cs`) to dynamically use `NEXUS_ADMIN_PASSWORD` from environment variables, falling back to a default password in local Development only.

3. **Feature-Flagged Restrictions**:
   - **`appsettings.Test.json`**: Implemented `Features:AllowRegistration` and `Features:AllowPasswordReset` flags set to `false`.
   - **Middleware Enforcement (`Program.cs`)**: Intercepts requests to `/identity/register` and `/identity/forgotPassword` (and their MVC/form variations) and rejects them with a `403 Forbidden` response in restricted environments.
   - **OAuth Provisioning Guard (`Program.cs`)**: Blocks new account provisioning via Google OAuth callback by checking the `Features:AllowRegistration` configuration, redirecting users to the login page with a descriptive error.
   - **UI Protection (`Login.razor`, `Register.razor`)**: Conditionally hides registration/password reset links and intercepts manual navigation attempts to `/account/register` by redirecting to login with a warning.

---------

Co-authored-by: Marek Jasiński <jasins.marek@gmail.com>
Reviewed-on: #56
Co-authored-by: Antigravity <antigravity@google.com>
Co-committed-by: Antigravity <antigravity@google.com>

src/NexusReader.UI.Shared/Components/Organisms/BookIngestionModal.razor.css

@@ -118,8 +118,9 @@
     z-index: 10;
 }
 
-/* Parsing State */
-.parsing-state {
+/* Parsing and Ingesting States */
+.parsing-state,
+.ingesting-state {
     flex: 1;
     display: flex;
     justify-content: center;
@@ -158,7 +159,8 @@
     filter: drop-shadow(0 0 8px rgba(0, 255, 153, 0.3));
 }
 
-.parsing-state p {
+.parsing-state p,
+.ingesting-state p {
     color: var(--nexus-text);
     font-family: var(--nexus-font-mono, monospace);
     font-size: 0.9rem;
@@ -371,10 +373,11 @@
     position: absolute;
     width: 20px;
     height: 20px;
-    border: 2px solid rgba(0, 0, 0, 0.1);
-    border-top-color: #000;
+    border: 2px solid rgba(255, 255, 255, 0.2);
+    border-top-color: var(--nexus-neon, #00ffaa);
     border-radius: 50%;
     animation: spin 0.8s linear infinite;
+    filter: drop-shadow(0 0 4px var(--nexus-neon, #00ffaa));
 }
 
 /* Indexing State */