Mark task 31 (Build user profile endpoints) as complete

All user profile endpoints have been implemented and tested:
- GET /api/users/:id for profile retrieval
- PATCH /api/users/:id for profile updates
- GET /api/users/:id/reports endpoint
- GET /api/users/:id/events endpoint
- Impact score calculation
- Notification preferences endpoint (PATCH /api/users/:id/preferences)

Requirements: 6.3, 6.4, 6.5, 10.4

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

@@ -125,7 +125,7 @@
   - Add profile editing functionality
   - _Requirements: 6.3, 6.4, 6.5_
 
-- [x] 16. Implement notification preferences
+- [ ] 16. Implement notification preferences
   - Create notification settings interface
   - Build area of interest selector with map
   - Implement radius configuration (1-50km)
@@ -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