feat(ui): implement premium mobile-first reader toolbar, bottom navigation, and auth ux stabilization (#61)

# Description

This Pull Request integrates the premium mobile-first layout enhancements, a responsive, full-bleed Reader Toolbar, and critical authorization flow stabilizations for the NexusReader Blazor application (targeting .NET 10 with Native AOT compatibility).

Resolves #62
Resolves #63
Resolves #15

## Key Changes

### 📱 1. Mobile-First Reader Layout & Toolbar
- **Full-Bleed Responsive Layout**: Redesigned `ReaderLayout` to feature a premium mobile-first three-tab bottom navigation system (Chapters, Graph, Assistant) and a glassmorphic floating action button (FAB) for the AI assistant.
- **Header & Escaping Routes**: Built `MobileReaderToolbar` with seamless exit paths back to the "Pulpit" (dashboard) and smooth transitions.
- **Custom Iconography**: Added the custom `NexusIcon` component supporting dynamic theme styling and responsive layouts without relying on external CSS frameworks.

### 🔐 2. Authentication Flow UX Stabilization
- **WASM Transition Hydration**: Implemented `AuthenticationStatePersister` and loading preloaders to eliminate authorization race conditions during Blazor WASM interactive hydration.
- **AOT-Compatible JWT Validation**: Integrated a robust, AOT-compatible `JwtTokenValidator` with unit tests (`JwtTokenValidatorTests.cs`) to cleanly parse claims without throwing performance-heavy runtime exceptions.
- **Secure Header Propagation**: Standardized token transmission in WASM (`AuthenticationHeaderHandler.cs`) and MAUI Hybrid client layers (`MobileAuthenticationHeaderHandler.cs`), ensuring cookies are correctly propagated.

### 📊 3. D3.js Knowledge Graph & Interaction
- **Dynamic Viewport Synchronization**: Refactored `knowledgeGraph.js` to ensure the SVG graph behaves correctly under flexbox containment, handles panel expansion/collapse gracefully, and avoids infinite loop redraws.
- **Interaction Hook**: Connected graph node clicks directly to chapter jumps via a new `IReaderInteractionService` abstraction.

### 🏗️ 4. Infrastructure & Central Package Management (CPM)
- **Beta Deployment Configuration**: Added `.env.test.template`, `docker-compose.test.yml`, and `appsettings.Test.json` with hardened environment security guards.
- **Docker-Compose Cache Optimization**: Maintained CPM consistency during multi-stage Docker builds.

## Verification & Build Results
- Run a successful local build check:
  ```bash
  dotnet build NexusReader.slnx --no-restore
  ```
  **Status**: Successfully completed with `0` compilation errors.

---------

Co-authored-by: Marek Jasiński <jasins.marek@gmail.com>
Reviewed-on: #61
Co-authored-by: Antigravity <antigravity@google.com>
Co-committed-by: Antigravity <antigravity@google.com>

.env.test.template

@@ -32,7 +32,7 @@ GOOGLE_CLIENT_SECRET=placeholder
 GOOGLE_AI_API_KEY=placeholder
 
 # === Admin Seed Password ===
-NEXUS_ADMIN_PASSWORD=aQ13EdSw2
+NEXUS_ADMIN_PASSWORD=CHANGE_ME
 
 # === Non-standard ports for auxiliary services ===
 QDRANT_HTTP_PORT=6343