chore: update test fixtures and frontend for UUID identity (refs #217)

Backend test fixtures:
- Replace auth0|xxx format with UUID in all test userId values
- Update admin tests for new id/userProfileId schema
- Add missing deletionRequestedAt/deletionScheduledFor to auth test mocks
- Fix admin integration test supertest usage (app.server)

Frontend:
- AdminUser type: auth0Sub -> id + userProfileId
- admin.api.ts: all user management methods use userId (UUID) params
- useUsers/useAdmins hooks: auth0Sub -> userId/id in mutations
- AdminUsersPage + AdminUsersMobileScreen: user.auth0Sub -> user.id
- Remove encodeURIComponent (UUIDs don't need encoding)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend/src/features/stations/tests/integration/community-stations.api.test.ts

@@ -12,8 +12,8 @@ describe('Community Stations API Integration Tests', () => {
   let app: FastifyInstance;
   let pool: Pool;
 
-  const testUserId = 'auth0|test-user-123';
-  const testAdminId = 'auth0|test-admin-123';
+  const testUserId = '550e8400-e29b-41d4-a716-446655440000';
+  const testAdminId = '7c9e6679-7425-40de-944b-e07fc1f90ae7';
 
   const mockStationData = {
     name: 'Test Gas Station',