Refactor and centralize user and pagination interfaces in useAdmin hook

- Unified `User` and `PaginationMeta` type definitions into `useAdmin` to improve maintainability and consistency.
- Updated affected components (`UserManagementContent`, `UserListTable`, `UserFormDialog`, `UserActionMenu`) to reference the centralized types.
- Enhanced test coverage for user-related hooks to include create, update, delete, activate, deactivate, and bulk actions.

frontend/src/components/admin/users/UserFormDialog.tsx

@@ -26,6 +26,7 @@ import { toast } from 'sonner';
 import {
   useCreateUser,
   useUpdateUser,
+  type User,
 } from '@/lib/api/hooks/useAdmin';
 
 // ============================================================================
@@ -58,15 +59,6 @@ type UserFormData = z.infer<typeof userFormSchema>;
 // Component
 // ============================================================================
 
-interface User {
-  id: string;
-  email: string;
-  first_name: string;
-  last_name: string | null;
-  is_active: boolean;
-  is_superuser: boolean;
-}
-
 interface UserFormDialogProps {
   open: boolean;
   onOpenChange: (open: boolean) => void;