Add User Management component to admin page, replacing placeholder text with functional UI for user management.

app/admin/page.tsx

@@ -5,6 +5,7 @@ import { useSession } from "next-auth/react";
 import { useRouter } from "next/navigation";
 import Navigation from "@/components/Navigation";
 import ImageSelector from "@/components/ImageSelector";
+import UserManagement from "@/components/UserManagement";
 
 interface SitePreferences {
   id: string;
@@ -241,9 +242,7 @@ export default function AdminPage() {
               <h2 className="text-2xl font-gaming font-bold mb-6 text-pixel-gold">
                 Gestion des Utilisateurs
               </h2>
-              <div className="text-center text-gray-400 py-8">
-                Section utilisateurs à venir...
-              </div>
+              <UserManagement />
             </div>
           )}
         </div>