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>

frontend/src/features/admin/__tests__/AdminUsersPage.test.tsx

@@ -48,7 +48,8 @@ describe('AdminUsersPage', () => {
     mockUseAdminAccess.mockReturnValue({
       isAdmin: true,
       adminRecord: {
-        auth0Sub: 'auth0|123',
+        id: 'admin-uuid-123',
+        userProfileId: 'user-uuid-123',
         email: 'admin@example.com',
         role: 'admin',
         createdAt: '2024-01-01',