feat(ui/arch): Optimize Graph Dynamics, Immersive Reader, and Core Stability (#19)

This PR introduces a major optimization of graph dynamics, immersive reading experience, and architectural stabilization.

### 🚀 Key Improvements

- **Knowledge Graph (Fix #16)**:
  - Implemented smooth D3.js transitions using the General Update Pattern.
  - Added "Neon Flash" entry animations and dynamic node dimming for better focus.
- **Immersive Reader (Fix #12)**:
  - Standardized centered layout (`max-width: 800px`) with **Merriweather** typography.
  - Optimized line-height and letter-spacing for premium readability.
- **Technical Code Blocks (Fix #20)**:
  - High-contrast dark containers for code snippets.
  - **JetBrains Mono** integration and neon-accented scrollbars.
- **Architectural Stabilization**:
  - Enforced a strict **'no async void'** policy in UI services using `Func<Task>`.
  - Resolved WASM runtime DI errors by implementing dummy service proxies for server-side dependencies.
  - Replaced generic 'Not Found' message with a branded Nexus preloader.

Fixes #7, Fixes #12, Fixes #16, Fixes #20.

Reviewed-on: #19
Co-authored-by: Marek Jasiński <jasins.marek@gmail.com>
Co-committed-by: Marek Jasiński <jasins.marek@gmail.com>

src/NexusReader.UI.Shared/Services/FocusModeService.cs

@@ -6,7 +6,7 @@ public sealed class FocusModeService : IFocusModeService
 {
     private readonly IJSRuntime _jsRuntime;
     public bool IsFocusModeActive { get; private set; }
-    public event Action? OnFocusModeChanged;
+    public event Func<Task>? OnFocusModeChanged;
 
     public FocusModeService(IJSRuntime jsRuntime)
     {
@@ -21,7 +21,7 @@ public sealed class FocusModeService : IFocusModeService
             if (value == "true" && !IsFocusModeActive)
             {
                 IsFocusModeActive = true;
-                OnFocusModeChanged?.Invoke();
+                if (OnFocusModeChanged != null) await OnFocusModeChanged();
             }
         }
         catch
@@ -33,7 +33,7 @@ public sealed class FocusModeService : IFocusModeService
     public async Task ToggleAsync()
     {
         IsFocusModeActive = !IsFocusModeActive;
-        OnFocusModeChanged?.Invoke();
+        if (OnFocusModeChanged != null) await OnFocusModeChanged();
 
         try
         {