fix playground for v1 (#799)

# What does this PR do?

- update playground callsites for v1 api changes

## Test Plan

```
cd llama_stack/distribution/ui
streamlit run app.py
```


https://github.com/user-attachments/assets/eace11c6-600a-42dc-b4e7-6948a706509f




## Sources

Please link relevant resources if necessary.


## Before submitting

- [ ] This PR fixes a typo or improves the docs (you can dismiss the
other checks if that's the case).
- [ ] Ran pre-commit to handle lint / formatting issues.
- [ ] Read the [contributor
guideline](https://github.com/meta-llama/llama-stack/blob/main/CONTRIBUTING.md),
      Pull Request section?
- [ ] Updated relevant documentation.
- [ ] Wrote necessary unit or integration tests.

llama_stack/distribution/ui/page/distribution/datasets.py

@@ -14,6 +14,6 @@ def datasets():
     datasets_info = {
         d.identifier: d.to_dict() for d in llama_stack_api.client.datasets.list()
     }
-
-    selected_dataset = st.selectbox("Select a dataset", list(datasets_info.keys()))
-    st.json(datasets_info[selected_dataset], expanded=True)
+    if len(datasets_info) > 0:
+        selected_dataset = st.selectbox("Select a dataset", list(datasets_info.keys()))
+        st.json(datasets_info[selected_dataset], expanded=True)