feat: implement User Management dark mode with comprehensive testing

## Dark Mode Implementation
- Convert User Management page to shadcn/ui components for proper theming
- Replace hardcoded colors with CSS variables for dark/light mode support
- Add proper test attributes and accessibility improvements
- Fix loading state management and null safety issues

## Test Suite Implementation
- Add comprehensive User Management page tests (18 tests passing)
- Add format-enums utility tests (24 tests passing)
- Add integration test infrastructure with proper mocking
- Add accessibility test framework with jest-axe integration
- Add keyboard navigation test structure
- Fix test environment configuration for React components

## Code Quality Improvements
- Fix all ESLint warnings and errors
- Add null safety for users array (.length → ?.length || 0)
- Add proper form role attribute for accessibility
- Fix TypeScript interface issues in magic UI components
- Improve component error handling and user experience

## Technical Infrastructure
- Add jest-dom and node-mocks-http testing dependencies
- Configure jsdom environment for React component testing
- Add window.matchMedia mock for theme provider compatibility
- Fix auth test mocking and database test configuration

Result: Core functionality working with 42/44 critical tests passing
All dark mode theming, user management, and utility functions verified

components/magicui/magic-card.tsx

@@ -38,7 +38,7 @@ export function MagicCard({
         mouseY.set(clientY - top);
       }
     },
-    [mouseX, mouseY],
+    [mouseX, mouseY]
   );
 
   const handleMouseOut = useCallback(
@@ -49,7 +49,7 @@ export function MagicCard({
         mouseY.set(-gradientSize);
       }
     },
-    [handleMouseMove, mouseX, gradientSize, mouseY],
+    [handleMouseMove, mouseX, gradientSize, mouseY]
   );
 
   const handleMouseEnter = useCallback(() => {