add deleted attribute

lib/data/models/group.dart

@@ -8,6 +8,7 @@ class Group {
   final String description;
   final DateTime createdAt;
   final List<Player> members;
+  final bool deleted;
 
   Group({
     String? id,
@@ -15,6 +16,7 @@ class Group {
     required this.name,
     String? description,
     required this.members,
+    this.deleted = false,
   }) : id = id ?? const Uuid().v4(),
        createdAt = createdAt ?? clock.now(),
        description = description ?? '';
@@ -31,7 +33,8 @@ class Group {
       createdAt = DateTime.parse(json['createdAt']),
       name = json['name'],
       description = json['description'],
-      members = [];
+      members = [],
+      deleted = json['deleted'] ?? false;
 
   /// Converts the Group instance to a JSON object. Related [Player] objects are
   /// represented by their IDs.
@@ -41,5 +44,6 @@ class Group {
     'name': name,
     'description': description,
     'memberIds': members.map((member) => member.id).toList(),
+    'deleted': deleted,
   };
 }