feat(100): bandeau dashboard générique, icônes rôle/email, footer go_router, user fromJson défensif

- Bandeau générique DashboardBandeau (logo | onglets | capsule utilisateur)
- Capsule: icône rôle (admin/gestionnaire/parent/AM) + Prénom Nom + menu (email avec icône, Profil, Paramètres, Déconnexion)
- Migration admin, gestionnaire, parent, AM vers DashboardBandeau
- Écran AM (page blanche), route /am-dashboard
- Routes /privacy et /legal, footer avec context.push
- AppUser.fromJson: id/email/role null-safe
- Suppression DashboardAppBarAdmin et dashboard_app_bar.dart

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

frontend/lib/config/app_router.dart

@@ -22,6 +22,9 @@ import '../screens/home/home_screen.dart';
 import '../screens/administrateurs/admin_dashboardScreen.dart';
 import '../screens/gestionnaire/gestionnaire_dashboard_screen.dart';
 import '../screens/home/parent_screen/ParentDashboardScreen.dart';
+import '../screens/am/am_dashboard_screen.dart';
+import '../screens/legal/privacy_page.dart';
+import '../screens/legal/legal_page.dart';
 import '../screens/unknown_screen.dart';
 
 // --- Provider Instances ---
@@ -64,7 +67,16 @@ class AppRouter {
       ),
       GoRoute(
         path: '/am-dashboard',
-        builder: (BuildContext context, GoRouterState state) => const HomeScreen(),
+        builder: (BuildContext context, GoRouterState state) =>
+            const AmDashboardScreen(),
+      ),
+      GoRoute(
+        path: '/privacy',
+        builder: (BuildContext context, GoRouterState state) => const PrivacyPage(),
+      ),
+      GoRoute(
+        path: '/legal',
+        builder: (BuildContext context, GoRouterState state) => const LegalPage(),
       ),
 
       // --- Parent Registration Flow ---