[Helm] Missing volume mount in chart

Hi,

I noticed that the `volumeMounts` is missing when there is persistent volume usage within the StatefulSet: :

https://github.com/briefercloud/briefer/blob/main/chart/templates/jupyter-statefulset.yaml
```
volumeMounts:
- name: jupyter-storage
mountPath: /home/jupyteruser
```

Without this, all saved data will be lost when the pod is restarted.

Start with chart/templates/jupyter-statefulset.yaml and inspect the StatefulSet rendered when persistent volume usage is enabled. Confirm the jupyter-storage volume is mounted at /home/jupyteruser, then render or validate the Helm chart to verify the mount appears and saved data remains backed by the persistent volume.

Written by the indexing model from the issue text.