Support quotas for sandbox volumes

Hi,

I've been experimenting with the recently added persistent volume feature and noticed that there are currently no quota controls in place.

Specifically:

• A sandbox can write unlimited data to a mounted volume — FSStat reports ~4.6 EB of available space regardless of actual storage
• There's no way to set a maximum size per volume
• There's no limit on the number of volumes a team can create

Would you consider adding quota support? Some useful controls might include:

• Per-volume size cap — a configurable maximum byte limit per volume, enforced at the NFS layer or via filesystem-level quotas on the host
• Volume count limit per team — a cap on how many volumes a single team can create

For self-hosted deployments this is especially important when multiple teams share the same underlying storage, as a single runaway sandbox could exhaust the entire shared filesystem.

Thanks for the great work on this feature!