feat(#44): dashboard gestionnaire + redirection login rôle gestionnaire

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

frontend/lib/widgets/admin/dashboard_admin.dart

@@ -3,17 +3,22 @@ import 'package:go_router/go_router.dart';
 import 'package:p_tits_pas/services/auth_service.dart';
 
 /// Barre du dashboard admin : onglets Gestion des utilisateurs | Paramètres + déconnexion.
+/// Pour le dashboard gestionnaire : [showSettingsTab] = false, [roleLabel] = 'Gestionnaire'.
 class DashboardAppBarAdmin extends StatelessWidget
     implements PreferredSizeWidget {
   final int selectedIndex;
   final ValueChanged<int> onTabChange;
   final bool setupCompleted;
+  final bool showSettingsTab;
+  final String roleLabel;
 
   const DashboardAppBarAdmin({
     Key? key,
     required this.selectedIndex,
     required this.onTabChange,
     this.setupCompleted = true,
+    this.showSettingsTab = true,
+    this.roleLabel = 'Admin',
   }) : super(key: key);
 
   @override
@@ -39,8 +44,10 @@ class DashboardAppBarAdmin extends StatelessWidget
                 children: [
                   _buildNavItem(context, 'Gestion des utilisateurs', 0,
                       enabled: setupCompleted),
-                  const SizedBox(width: 24),
-                  _buildNavItem(context, 'Paramètres', 1, enabled: true),
+                  if (showSettingsTab) ...[
+                    const SizedBox(width: 24),
+                    _buildNavItem(context, 'Paramètres', 1, enabled: true),
+                  ],
                 ],
               ),
             ),
@@ -48,12 +55,12 @@ class DashboardAppBarAdmin extends StatelessWidget
         ],
       ),
       actions: [
-        const Padding(
-          padding: EdgeInsets.symmetric(horizontal: 16),
+        Padding(
+          padding: const EdgeInsets.symmetric(horizontal: 16),
           child: Center(
             child: Text(
-              'Admin',
-              style: TextStyle(
+              roleLabel,
+              style: const TextStyle(
                 color: Colors.black,
                 fontSize: 16,
                 fontWeight: FontWeight.w500,