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/src/components/__tests__/club-switcher.test.tsx

@@ -22,7 +22,7 @@ describe('ClubSwitcher', () => {
   });
 
   it('renders loading state when clubs is empty', () => {
-    vi.mocked(useTenant).mockReturnValue({
+    (useTenant as any).mockReturnValue({
       activeClubId: null,
       clubs: [],
       setActiveClub: vi.fn(),
@@ -34,7 +34,7 @@ describe('ClubSwitcher', () => {
   });
 
   it('renders current club name and sport type badge', () => {
-    vi.mocked(useTenant).mockReturnValue({
+    (useTenant as any).mockReturnValue({
       activeClubId: 'club-1',
       clubs: [
         { id: 'club-1', name: 'Tennis Club', sportType: 'Tennis' },
@@ -50,7 +50,7 @@ describe('ClubSwitcher', () => {
 
   it('calls setActiveClub when club is selected', () => {
     const mockSetActiveClub = vi.fn();
-    vi.mocked(useTenant).mockReturnValue({
+    (useTenant as any).mockReturnValue({
       activeClubId: 'club-1',
       clubs: [
         { id: 'club-1', name: 'Tennis Club', sportType: 'Tennis' },