refactor: Extract reusable UI components and add TDD documentation

- Add comprehensive TDD documentation to CLAUDE.md with coverage requirements and examples
- Extract reusable UI components to frontend/src/components/ui/ (Modal, FormInput, Button, Alert, etc.)
- Add shared constants (schedulePresets) and utility hooks (useCrudMutation, useFormValidation)
- Update frontend/CLAUDE.md with component documentation and usage examples
- Refactor CreateTaskModal to use shared components and constants
- Fix test assertions to be more robust and accurate across all test files

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

frontend/src/hooks/__tests__/useResources.test.ts

@@ -137,13 +137,12 @@ describe('useResources hooks', () => {
       expect(apiClient.post).toHaveBeenCalledWith('/resources/', {
         name: 'New Room',
         type: 'ROOM',
-        user: null,
-        timezone: 'UTC',
+        user_id: null,
         max_concurrent_events: 3,
       });
     });
 
-    it('converts userId to user integer', async () => {
+    it('converts userId to user_id integer', async () => {
       vi.mocked(apiClient.post).mockResolvedValue({ data: { id: 1 } });
 
       const { result } = renderHook(() => useCreateResource(), {
@@ -159,7 +158,7 @@ describe('useResources hooks', () => {
       });
 
       expect(apiClient.post).toHaveBeenCalledWith('/resources/', expect.objectContaining({
-        user: 42,
+        user_id: 42,
       }));
     });
   });