dispose model controller and end AI client

Frontend/lib/mih_packages/mzansi_ai/ai_chat.dart

@@ -166,6 +166,14 @@ class _AiChatState extends State<AiChat> {
     );
   }
 
+  @override
+  void dispose() {
+    // TODO: implement dispose
+    super.dispose();
+    _modelCopntroller.dispose();
+    client.endSession();
+  }
+
   @override
   void initState() {
     super.initState();