Merge develop: fix auth connexion admin (#84)

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

frontend/lib/models/user.dart

@@ -20,8 +20,12 @@ class AppUser {
       id: json['id'] as String,
       email: json['email'] as String,
       role: json['role'] as String,
-      createdAt: DateTime.parse(json['createdAt'] as String),
-      updatedAt: DateTime.parse(json['updatedAt'] as String),
+      createdAt: json['createdAt'] != null
+          ? DateTime.parse(json['createdAt'] as String)
+          : DateTime.now(),
+      updatedAt: json['updatedAt'] != null
+          ? DateTime.parse(json['updatedAt'] as String)
+          : DateTime.now(),
       changementMdpObligatoire: json['changement_mdp_obligatoire'] as bool? ?? false,
     );
   }