fix(test): replace vi.mocked with type casting for Bun compatibility

Fixes technical debt from Tasks 10, 18-20.

Problem:
- 38/46 frontend tests failing due to vi.mocked() not supported in Bun
- happy-dom environment causing document errors in some tests

Solution:
1. Replaced all vi.mocked(fn) calls with (fn as any) type casting
   - useActiveClub.test.ts: 3 occurrences (localStorage mocks)
   - auth-guard.test.tsx: 13 occurrences (useSession, useTenant, useRouter)
   - club-switcher.test.tsx: 3 occurrences (useRouter)
   - task-detail.test.tsx: 4 occurrences (useRouter, useTasks)
   - task-list.test.tsx: 1 occurrence (useTasks)

2. Updated vitest.config.ts:
   - Changed environment from happy-dom to jsdom (better DOM support)
   - Added exclude pattern to prevent e2e tests interference

Test Results:
- Before: 8/46 passing (38 failures)
- After: 45/45 passing (0 failures) ✅

No source code changes - only test infrastructure fixes.

frontend/vitest.config.ts

@@ -5,9 +5,10 @@ import path from 'path';
 export default defineConfig({
   plugins: [react()],
   test: {
-    environment: 'happy-dom',
+    environment: 'jsdom',
     globals: true,
     setupFiles: ['./src/test/setup.ts'],
+    exclude: ['node_modules', 'dist', '.idea', '.git', '.cache', 'e2e'],
   },
   resolve: {
     alias: {