Replace spinners with skeleton loading states for faster perceived UX.

Add reusable Skeleton components and route-level loading files across public pages and admin lists so layouts stay stable while data loads.

Co-authored-by: Cursor <cursoragent@cursor.com>

frontend/src/app/admin/users/page.tsx

@@ -6,6 +6,7 @@ import { usersApi, eventsApi, User, Event } from '@/lib/api';
 import { parseDate } from '@/lib/utils';
 import Card from '@/components/ui/Card';
 import Button from '@/components/ui/Button';
+import { AdminPageSkeleton } from '@/components/ui/Skeleton';
 import Input from '@/components/ui/Input';
 import { MoreMenu, DropdownItem, BottomSheet, AdminMobileStyles } from '@/components/admin/MobileComponents';
 import { TrashIcon, PencilSquareIcon, FunnelIcon, XMarkIcon, MagnifyingGlassIcon } from '@heroicons/react/24/outline';
@@ -166,11 +167,7 @@ export default function AdminUsersPage() {
   };
 
   if (loading) {
-    return (
-      <div className="flex items-center justify-center py-12">
-        <div className="animate-spin w-8 h-8 border-4 border-primary-yellow border-t-transparent rounded-full" />
-      </div>
-    );
+    return <AdminPageSkeleton cols={6} />;
   }
 
   return (