feat(ui/graph): optimize graph dynamics, immersive reader, and code blocks

- Fix #16: Implement D3.js transitions and active state badges for Knowledge Graph.
- Fix #12: Implement Immersive Reader Layout with Merriweather typography.
- Fix #20: Professional code block styling with high contrast and monospace fonts.
- Resolve DI runtime error in WASM by adding dummy services.
- Replace generic 'Not Found' message with Nexus preloader.
- Enforce 'no async void' architecture across UI services.

src/NexusReader.UI.Shared/Components/Molecules/IntelligenceToolbar.razor

@@ -42,7 +42,7 @@
 @code {
     protected override void OnInitialized()
     {
-        FocusMode.OnFocusModeChanged += StateHasChanged;
+        FocusMode.OnFocusModeChanged += HandleUpdate;
     }
 
     private async Task HandleClearCache()
@@ -56,8 +56,10 @@
         }
     }
 
+    private Task HandleUpdate() => InvokeAsync(StateHasChanged);
+
     public void Dispose()
     {
-        FocusMode.OnFocusModeChanged -= StateHasChanged;
+        FocusMode.OnFocusModeChanged -= HandleUpdate;
     }
 }