feat: enhance admin management UI and functionality

- Refactor role-permission mapping component to use ChangeDetectionStrategy.OnPush for better performance.
- Update roles component to include loading indicators and improved error handling.
- Revamp user roles management UI with a new layout and enhanced user experience.
- Implement confirmation dialogs for user and role deletions to prevent accidental actions.
- Improve user management interface with better form validation and user feedback.
- Add skeleton loading states for better UX during data fetching.

Author: nitin27may

frontend/.github/copilot-design-checklist.md

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+# Design Quality Checklist
+
+Use this checklist before committing any UI component:
+
+## Visual Consistency
+- [ ] Spacing uses 8px grid (4, 8, 16, 24, 32, 48, 64)
+- [ ] Colors from theme palette (no hardcoded hex)
+- [ ] Typography follows Material scale
+- [ ] Consistent elevation (0, 1, 2, 4, 8)
+- [ ] Border radius consistent (sm/md/lg)
+
+## Responsiveness
+- [ ] Works on mobile (< 600px)
+- [ ] Works on tablet (600-960px)
+- [ ] Works on desktop (> 960px)
+- [ ] Touch targets minimum 44x44px
+- [ ] Text readable at all sizes
+
+## Theme Support
+- [ ] Light theme perfect
+- [ ] Dark theme perfect
+- [ ] No hardcoded colors
+- [ ] Proper contrast (WCAG AA)
+- [ ] Icons/borders adapt
+
+## Code Quality
+- [ ] Standalone component
+- [ ] OnPush change detection
+- [ ] Signals for state
+- [ ] New control flow syntax
+- [ ] Proper TypeScript types
+- [ ] No any types
+- [ ] ARIA labels present
+
+## Performance
+- [ ] Lazy loading where appropriate
+- [ ] Track by in loops
+- [ ] No unnecessary re-renders
+- [ ] Optimized imports