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/border-beam.tsx

@@ -66,15 +66,17 @@ export const BorderBeam = ({
   return (
     <div
       className="pointer-events-none absolute inset-0 rounded-[inherit] border-transparent [mask-clip:padding-box,border-box] [mask-composite:intersect] [mask-image:linear-gradient(transparent,transparent),linear-gradient(#000,#000)] border-(length:--border-beam-width)"
-      style={{
-        "--border-beam-width": `${borderWidth}px`,
-      } as React.CSSProperties}
+      style={
+        {
+          "--border-beam-width": `${borderWidth}px`,
+        } as React.CSSProperties
+      }
     >
       <motion.div
         className={cn(
           "absolute aspect-square",
           "bg-gradient-to-l from-[var(--color-from)] via-[var(--color-to)] to-transparent",
-          className,
+          className
         )}
         style={
           {