MinIO's images no longer pull, so object storage is now the Garage
template. Attach storage creates a bucket named for the app and a key
that can read and write only that bucket, keeps the secret in an
internal vault, and wires S3_* and AWS_* env through fromService and
fromSecret. Detach revokes the key and removes the env but keeps the
bucket and its objects. A docker leg proves the scope against a
real Garage.
