fix: add support for Clerk IDs and activity endpoint

- Update getUserProfile to accept both database ID and Clerk ID
- Update getUserReports to handle Clerk IDs
- Update getUserEvents to handle Clerk IDs
- Add getUserActivity endpoint to return timeline of user actions
- Add activity route GET /api/users/:id/activity
- Fix TypeScript errors with const assertions

This fixes 404 errors when frontend uses Clerk IDs to fetch user data

.kiro/specs/beach-litter-mapping/tasks.md

@@ -259,7 +259,7 @@
   - Create verification audit log
   - _Requirements: 7.1, 7.2, 7.3, 7.4, 7.5_
 
-- [-] 31. Build user profile endpoints
+- [x] 31. Build user profile endpoints
   - Create GET /api/users/:id for profile retrieval
   - Implement PATCH /api/users/:id for profile updates
   - Build GET /api/users/:id/reports endpoint