feat: Implement group management features with Firestore integration and loading states

lib/models/message.dart

@@ -0,0 +1,13 @@
+class Message {
+  final String text; 
+  final DateTime timestamp;
+  final String senderId;
+  final String senderName;
+
+  Message({
+    required this.text,
+    required this.timestamp,
+    required this.senderId,
+    required this.senderName,
+  });
+}