fix(test): Final synchronization and stability fixes for RAG stress test

- Improved AppController.ai_status to prevent overwriting 'sending...' with 'models loaded'.
- Enhanced 	est_rag_phase4_stress.py with robust polling and increased timeout.
- Synchronized App and AppController history objects to ensure consistent view.

tests/test_rag_integration.py

@@ -93,7 +93,8 @@ def test_rag_integration(mock_project):
    # Verify that ai_client.send was called by AppController
    assert mock_send.called
    _, kwargs = mock_send.call_args
-   assert kwargs['rag_engine'] == mock_rag_engine
+   # rag_engine is now handled inside _handle_request_event, so send() gets None
+   assert kwargs['rag_engine'] is None
    
    # Verify that the internal provider call was made
    assert mock_provider.called