Refactor user and theme management to use BLoC pattern; remove provider classes and integrate new services for user and group functionalities

lib/services/group_service.dart

@@ -1,5 +1,5 @@
 import 'package:cloud_firestore/cloud_firestore.dart';
-import 'package:travel_mate/models/group.dart';
+import 'package:travel_mate/data/models/group.dart';
 
 class GroupService {
   final FirebaseFirestore _firestore = FirebaseFirestore.instance;
@@ -57,4 +57,14 @@ class GroupService {
       }).toList();
     });
   }
+
+  Future<void> removeMemberFromGroup(String groupId, String memberId) async {
+    // TODO: Implémenter la suppression d'un membre d'un groupe
+  }
+
+  Future<void> addMemberToGroup(String groupId, String memberId) async {
+    // TODO: Implémenter l'ajout d'un membre à un groupe
+  }
+
+
 }