feat(ui): implement premium gamified Concepts Map dashboard, unify design tokens, and enforce scoped CSS (#54)

Resolves #55

# gamified Concepts Map Dashboard, Architecture Cleanup, & CSS Unification

This Pull Request completes the gamified **Concepts Map** interactive experience and executes a strict visual and architectural clean-up of the **NexusReader SaaS** platform by consolidating styling around the centralized **Nexus Neon** design system, enforcing Native AOT-compliant scoped-CSS, and resolving style drift.

---

### 🚀 Key Implementations

#### 1. Gamified Interactive Concepts Map Dashboard
* **Dynamic Skill-Tree Visualizer:** Implemented a gamified node-based interactive tree that reads concept connections dynamically, rendering progress nodes, unlocked/locked states, and active visual connection lines.
* **Premium UX Details:** Integrated high-fidelity hover effects, detailed sidebar popovers showing unlocked stats/summaries, and smooth parallax backdrops.
* **Secure Multi-Tenant Gating:** Hardened data queries using explicit `TenantId` gating to ensure complete layout isolation between system tenants.

#### 2. Architecture & Service Optimization
* **Service Abstraction (`IConceptsMapService`):** Introduced a clean service interface decoupled from the UI layers.
* **Polyglot Fallback Implementations:**
  - **WasmConceptsMapService:** Implements efficient client-side fetching with error recovery/loading states.
  - **ServerConceptsMapService:** Handles deep database graph mapping, relationship resolution, and multi-tenant checks.
* **CQRS Integrity:** Enforced the CQRS Result Pattern by using `MediatR` handlers to fetch data structures instead of placing database queries in UI modules.

#### 3. Nexus Neon CSS Unification & Zero-Style-Tag Standards
* **Central Design Tokens:** Solidified typography (`Inter` / `Merriweather`), primary brand green hues (`var(--nexus-neon)` at `#00ff99`), and glow variables inside the global `app.css`.
* **Zero Inline Style Tags:** Standardized all dashboard modules by completely eliminating inline `<style>` blocks in favor of scoped `.razor.css` companion files.
* **Consolidated Buttons & Glass Panels:**
  - Standardized `.btn-nexus`, `.btn-nexus-primary`, and `.btn-nexus-secondary` throughout header/footer/card operations.
  - Removed duplicate `.glass-panel` background, blur, and support-declaration overrides, making components cleanly inherit standard global styles.
* **Eliminated Brand Splitting:** Resolved legacy purple-indigo user avatar and conversation bubble gradients inside the AI Intelligence Hub (`Intelligence.razor.css`), migrating them to premium glassmorphic surfaces (`rgba(255, 255, 255, 0.05)`) contrasting beautifully against the emerald green AI theme.

---

### 🧪 Verification & Build Gate Status

* **Successful Compilation Check:** Run `dotnet build NexusReader.slnx --no-restore` from the workspace root. Flawlessly succeeded with **zero compilation errors** (`Liczba błędów: 0`) under target `.NET 10`.
* **Verified Skills Synchrony:** The companion design guidelines skill (`nexus-ui-engine/SKILL.md`) has been fully updated to secure these layout and styling conventions for future dashboard features.

---------

Co-authored-by: Marek Jasiński <jasins.marek@gmail.com>
Reviewed-on: #54
Co-authored-by: Antigravity <antigravity@google.com>
Co-committed-by: Antigravity <antigravity@google.com>

src/NexusReader.UI.Shared/wwwroot/app.css

@@ -2,6 +2,7 @@
 
 :root {
     --nexus-neon: #00ff99;
+    --nexus-neon-glow: rgba(0, 255, 153, 0.3);
     --nexus-bg: #121212;
     --nexus-card: #1a1a1a;
     --nexus-text: #ffffff;
@@ -9,6 +10,17 @@
     --nexus-font-sans: 'Inter', sans-serif;
     --nexus-font-serif: 'Merriweather', serif;
     
+    /* Global Semantic Theme Mapping */
+    --nexus-primary: var(--nexus-neon);
+    --nexus-primary-glow: var(--nexus-neon-glow);
+    --nexus-primary-hover: #00e688;
+    
+    /* Standard Layout Tokens */
+    --radius-sm: 8px;
+    --radius-md: 12px;
+    --radius-lg: 16px;
+    --radius-xl: 20px;
+    
     /* Safe Area Insets with fallbacks */
     --safe-area-inset-top: env(safe-area-inset-top, 0px);
     --safe-area-inset-bottom: env(safe-area-inset-bottom, 0px);
@@ -23,7 +35,7 @@
 .glass-panel {
     background: rgba(20, 20, 20, 0.85); /* Darker fallback for readability */
     border: 1px solid rgba(255, 255, 255, 0.05);
-    border-radius: 20px;
+    border-radius: var(--radius-xl);
     padding: 1.5rem;
     transition: all 0.3s cubic-bezier(0.4, 0, 0.2, 1);
 }
@@ -35,6 +47,40 @@
     }
 }
 
+/* Unified Enterprise Component Constraints */
+.btn-nexus {
+    font-family: var(--nexus-font-sans);
+    font-weight: 600;
+    border-radius: var(--radius-md);
+    transition: all 0.2s cubic-bezier(0.4, 0, 0.2, 1);
+    cursor: pointer;
+    display: inline-flex;
+    align-items: center;
+    justify-content: center;
+    gap: 0.5rem;
+    border: none;
+    text-decoration: none;
+}
+.btn-nexus-primary {
+    background: var(--nexus-neon);
+    color: #000000;
+}
+.btn-nexus-secondary {
+    background: rgba(255, 255, 255, 0.05);
+    border: 1px solid rgba(255, 255, 255, 0.1);
+    color: #ffffff;
+}
+.btn-nexus:hover {
+    transform: translateY(-2px);
+    filter: brightness(1.1);
+}
+.btn-nexus-primary:hover {
+    box-shadow: 0 4px 15px var(--nexus-primary-glow);
+}
+.btn-nexus-secondary:hover {
+    box-shadow: 0 4px 15px rgba(255, 255, 255, 0.05);
+}
+
 
 .theme-light {
     --nexus-bg: var(--nexus-paper);