fix: handle model dropdown refresh when custom models exist

- Set default value when refreshing models to avoid Gradio error
- Prevents 'Value not in choices' error when model list changes

lib/ui.py

@@ -30,7 +30,8 @@ def upload_model(zip_file, model_name):
 def refresh_models():
     """Refresh the models list."""
     models = list_models()
-    return gr.update(value=[[m] for m in models]), gr.update(choices=models)
+    default_value = models[0] if models else None
+    return gr.update(value=[[m] for m in models]), gr.update(choices=models, value=default_value)
 
 
 def toggle_autotune(enabled):