feat(frontend): add return checklist screen with shared checklist widgets

eme-frontend/lib/screens/restitution_select_screen.dart

@@ -5,6 +5,7 @@ import "../models/materiel_item.dart";
 import "../models/emprunt_item.dart";
 import "../widgets/ensup_top_bar.dart";
 import "../widgets/brand_corners.dart";
+import "checklist_retour_screen.dart";
 
 const _pcDell = MaterielItem(
   nom: "PC Dell Latitude 5420",
@@ -28,8 +29,8 @@ class RestitutionSelectScreen extends StatelessWidget {
   const RestitutionSelectScreen({super.key});
 
   void _restituer(BuildContext context, EmpruntItem emprunt) {
-    ScaffoldMessenger.of(context).showSnackBar(
-      SnackBar(content: Text("Checklist de retour de ${emprunt.materiel.nom} — écran à venir")),
+    Navigator.of(context).push(
+      MaterialPageRoute(builder: (_) => ChecklistRetourScreen(emprunt: emprunt)),
     );
   }