feat: implement Portal component and refactor modals to use it for improved positioning

assets/admin/pages/ClinicsPage.tsx

@@ -17,6 +17,7 @@ import type { ApiResponse, PaginatedResponse } from '../lib/api';
 import type { Clinic } from '../types';
 import { useAuthStore } from '../stores/authStore';
 import MobileInput from '../components/ui/MobileInput';
+import Portal from '../components/ui/Portal';
 import { formatDate, formatNumber, iranMobileSchema } from '../lib/utils';
 import Pagination from '../components/ui/Pagination';
 import ConfirmDialog from '../components/ui/ConfirmDialog';
@@ -244,6 +245,7 @@ export default function ClinicsPage() {
 
       {/* Add Modal */}
       {addOpen && (
+        <Portal>
         <div className="overlay" onClick={() => setAddOpen(false)}>
           <div className="modal" style={{ maxWidth: 420 }} onClick={(e) => e.stopPropagation()}>
             <div className="modal-head">
@@ -287,6 +289,7 @@ export default function ClinicsPage() {
             </form>
           </div>
         </div>
+        </Portal>
       )}
 
       <ConfirmDialog