The UmbraAudio side of the cross-machine contract: this node registers
with the UmbraTrans controller, polls for jobs, claims them under a
lease, and writes artifacts back over NFS.
* `umbraaudio/cluster/` - configuration, PostgreSQL access, node
registration and heartbeat, the job queue, artifact storage and NFS
mount management.
* `scripts/cluster_worker.py` - the CLI: `worker`, `check-cluster`,
`register-node`.
* `scripts/backup_system.sh` / `scripts/verify_backup.sh` - whole-system
backup and integrity verification.
* `.env` - the `UMBRA_CLUSTER__*` settings. `UMBRA_CLUSTER__PG_PASSWORD`
is deliberately empty; the password comes from the environment, not
from a committed file.
`k3s-agent.yaml` is NOT committed: it contains a K3s server join token.
It is now gitignored, and the token should be rotated if that file has
ever left this machine.
ruff clean on the whole package.