feat: Mobile-First Layout Redesign & D3.js Graph Stabilization (#58)

This PR implements a comprehensive mobile-first design overhaul for the Reader, Dashboard, and Navigation layouts.

### Key Accomplishments
1. **Dynamic Viewport Synchronization**: Installed robust `ResizeObserver` listener on the client side with automatic reactive toggling of `platform-mobile`/`platform-desktop` CSS classes.
2. **Tab Controller & Visibility Fixes**: Refactored visibility constraints in `ReaderLayout.razor.css` to prevent layout clipping and DOM bloat. Standardized the mobile tab content selectors to ensure active views display perfectly.
3. **D3.js Graph Stabilization**:
   * Added checks to bypass resize callbacks when the graph container is hidden (`clientWidth <= 0` or `clientHeight <= 0`).
   * Guarded coordination ticks, node focus transformations, and zoom transitions against `NaN` parameters.
4. **Interactive Mobile UX Enhancements**: Optimized touch target sizing (44px target bounds) and interactive transitions for a state-of-the-art visual presentation.

This has been successfully compiled and verified against the standard .NET 10 compilation gates.

---------

Co-authored-by: Marek Jasiński <jasins.marek@gmail.com>
Reviewed-on: #58
Co-authored-by: Antigravity <antigravity@google.com>
Co-committed-by: Antigravity <antigravity@google.com>

src/NexusReader.UI.Shared/Layout/ReaderLayout.razor.css

@@ -506,7 +506,7 @@ main {
 }
 
 .platform-mobile .nexus-mobile-reader-tabs {
-    display: block;
+    display: none; /* Keep hidden by default */
     width: 100vw;
     height: calc(100vh - 60px);
     position: absolute;
@@ -517,6 +517,11 @@ main {
     z-index: 15;
 }
 
+.app-container.platform-mobile.active-mobile-tab-graph .nexus-mobile-reader-tabs,
+.app-container.platform-mobile.active-mobile-tab-insight .nexus-mobile-reader-tabs {
+    display: block; /* Show only when graph or insight tabs are active */
+}
+
 .nexus-mobile-tab-content {
     display: none;
     width: 100%;