feat(ui/graph): Knowledge Graph Refinement and Sidebar Hierarchy (#25)

This PR addresses several UI/UX and architectural refinements for the Knowledge Graph and Intelligence Sidebar.

### Key Changes:
- **Knowledge Graph (#21, #22)**:
  - Implemented \"pill-shaped\" nodes with dynamic label truncation and SVG tooltips.
  - Added bound-constrained simulation to keep nodes within the viewport.
  - Integrated `ResizeObserver` for dynamic layout handling.
  - Implemented Zoom-to-Fit functionality.
  - Enforced unique concept IDs in AI prompts and hardened JS logic to prevent multi-selection bugs.
- **Intelligence Sidebar (#23)**:
  - Improved visual depth with a radial gradient background for the graph.
  - Increased sidebar divider contrast for better layering.
  - Transformed graph controls into a floating glassmorphism panel.
  - Relocated the \"Logout\" action to the toolbar bottom and rebranded it as \"Exit\".

Fixes #21
Fixes #22
Fixes #23

Reviewed-on: #25
Co-authored-by: Marek Jasiński <jasins.marek@gmail.com>
Co-committed-by: Marek Jasiński <jasins.marek@gmail.com>

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

@@ -12,28 +12,33 @@
 
 .graph-controls {
     position: absolute;
-    bottom: 1rem;
+    bottom: 1.5rem;
     right: 1.5rem;
     display: flex;
-    flex-direction: column;
-    gap: 0.5rem;
+    flex-direction: row;
+    gap: 0.25rem;
+    background: rgba(20, 20, 20, 0.4);
+    backdrop-filter: blur(12px);
+    padding: 0.35rem;
+    border-radius: 8px;
+    border: 1px solid rgba(255, 255, 255, 0.08);
+    box-shadow: 0 8px 32px rgba(0, 0, 0, 0.4);
     z-index: 10;
 }
 
 .zoom-btn {
-    width: 28px;
-    height: 28px;
-    background: rgba(18, 18, 18, 0.8);
-    backdrop-filter: blur(4px);
-    border: 1px solid rgba(255, 255, 255, 0.1);
-    border-radius: 4px;
-    color: #888;
-    font-size: 1rem;
+    width: 32px;
+    height: 32px;
+    background: rgba(255, 255, 255, 0.03);
+    border: 1px solid rgba(255, 255, 255, 0.05);
+    border-radius: 6px;
+    color: #aaa;
+    font-size: 1.1rem;
     cursor: pointer;
     display: flex;
     align-items: center;
     justify-content: center;
-    transition: all 0.2s ease;
+    transition: all 0.2s cubic-bezier(0.4, 0, 0.2, 1);
 }
 
 .zoom-btn:hover {