Introduce comprehensive user management functionality for admin

- Added React Query hooks for user-related actions: `useCreateUser`, `useUpdateUser`, `useDeleteUser`, `useActivateUser`, `useDeactivateUser`, and `useBulkUserAction`.
- Implemented primary user management components: `UserFormDialog`, `UserManagementContent`, `UserListTable`, `BulkActionToolbar`, and `UserActionMenu`.
- Replaced placeholder content on the Users page with full user management capabilities.
- Included role-based validation, search, pagination, filtering, and bulk operations.
- Enhanced form validation with `zod` schema for robust user input handling.
- Added feedback mechanisms (toasts and alert dialogs) for user actions.
- Improved UI accessibility and usability across the admin user management feature.

frontend/src/components/ui/button.tsx

@@ -2,7 +2,7 @@ import * as React from "react"
 import { Slot } from "@radix-ui/react-slot"
 import { cva, type VariantProps } from "class-variance-authority"
 
-import { cn } from "@/lib/utils"
+import { cn } from "@/lib/utils/index"
 
 const buttonVariants = cva(
   "inline-flex items-center justify-center gap-2 whitespace-nowrap rounded-md text-sm font-medium transition-colors focus-visible:outline-none focus-visible:ring-1 focus-visible:ring-ring disabled:pointer-events-none disabled:opacity-50 [&_svg]:pointer-events-none [&_svg]:size-4 [&_svg]:shrink-0",