feat: redesign admin panel with Lucide icons and modern styling

- Add lucide-react for SVG icons throughout the admin
- Redesign sidebar with gradient background, icons per nav item, and sticky layout
- Redesign topbar with cleaner user info display
- Redesign dashboard with icon-backed stat cards, gradient progress bars, activity feed
- Update AdminNavLink with icon support and new active state styling
- Improve table styling in admin-page CSS (rounded corners, hover, spacing)
- Clean up unused admin CSS

package.json

@@ -23,6 +23,7 @@
     "bcryptjs": "^3.0.2",
     "croner": "^10.0.1",
     "hash-wasm": "^4.12.0",
+    "lucide-react": "^1.23.0",
     "next": "^16.2.9",
     "next-auth": "5.0.0-beta.31",
     "next-intl": "^4.13.0",