feat(auth): implement role-based access control and user management features

frontend/app/admin/users/page.tsx

@@ -0,0 +1,30 @@
+import { auth } from '../../../../auth';
+import { redirect } from 'next/navigation';
+import { fetchJson } from '../../../lib/api';
+import UserAdminClient from './UserAdminClient';
+
+type User = {
+  id: number;
+  username: string;
+  email: string;
+  firstName: string | null;
+  lastName: string | null;
+  role: string;
+  createdAt: string;
+};
+
+export default async function AdminUsersPage() {
+  const session = await auth();
+  if (!session || (session.user as any)?.role !== 'admin') {
+    redirect('/');
+  }
+
+  const users = await fetchJson<User[]>('/api/users');
+
+  return (
+    <main className="p-6 max-w-4xl mx-auto">
+      <h1 className="text-2xl font-bold mb-6">Användarhantering</h1>
+      <UserAdminClient users={users} currentUserId={session.user.id} />
+    </main>
+  );
+}