Stage-scope the volume bucket prefix (boxlite-volume-* is account-global)

[DorianZheng]

Problem

Volume bucket names are account-global, not stage-scoped: Volume.getBucketName() returns boxlite-volume-${id} (apps/api/src/box/entities/volume.entity.ts:48), while multiple stages (dev, e2e-ci, personal) share one AWS account.

Because the bucket name is the only stage signal available to IAM, every policy that scopes to arn:aws:s3:::boxlite-volume-* — the Api task role's volume statement and the runner's RunnerVolumeS3Policy (apps/infra/sst.config.ts) — necessarily spans all stages' volume buckets. Concretely: dev's API/runner can list, read, and delete e2e-ci's volume buckets, and vice versa. PR #732 narrowed the actions on these grants but could not narrow the resources further without this rename.

Proposed fix

1. Make the prefix configurable: VOLUME_BUCKET_PREFIX env (default boxlite-volume- for compatibility), set from sst.config.ts as ${$app.name}-${$app.stage}-volume-.
2. Persist bucketName on the volume row at creation time so existing volumes keep their current buckets while new volumes get the stage-scoped prefix (avoids orphaning boxlite-volume-<id> buckets already in use).
3. Tighten both IAM resource patterns to the stage prefix once the fleet of old-prefix volumes drains (or keep a temporary dual-pattern grant during transition).

Notes

• Bucket names are globally unique across AWS; the UUID suffix already prevents collisions — this is purely an isolation/IAM-scoping concern.
• The runner mounts buckets by name received from the control plane (apps/runner/pkg/boxlite/volumes.go), so no runner code change is needed beyond the IAM pattern.