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/core/middleware/require-tier.test.ts

@@ -17,7 +17,7 @@ const createRequest = (subscriptionTier?: string): Partial<FastifyRequest> => {
   }
   return {
     userContext: {
-      userId: 'auth0|user123456789',
+      userId: '550e8400-e29b-41d4-a716-446655440000',
       email: 'user@example.com',
       emailVerified: true,
       onboardingCompleted: true,