- 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
