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

e2e/example.spec.ts

@@ -1,18 +1,20 @@
-import { test, expect } from '@playwright/test';
+import { test, expect } from "@playwright/test";
 
-test('has title', async ({ page }) => {
-  await page.goto('https://playwright.dev/');
+test("has title", async ({ page }) => {
+  await page.goto("https://playwright.dev/");
 
   // Expect a title "to contain" a substring.
   await expect(page).toHaveTitle(/Playwright/);
 });
 
-test('get started link', async ({ page }) => {
-  await page.goto('https://playwright.dev/');
+test("get started link", async ({ page }) => {
+  await page.goto("https://playwright.dev/");
 
   // Click the get started link.
-  await page.getByRole('link', { name: 'Get started' }).click();
+  await page.getByRole("link", { name: "Get started" }).click();
 
   // Expects page to have a heading with the name of Installation.
-  await expect(page.getByRole('heading', { name: 'Installation' })).toBeVisible();
+  await expect(
+    page.getByRole("heading", { name: "Installation" })
+  ).toBeVisible();
 });