The `storage:list <app> --format json` payload conflated the
attachment's `Readonly` flag and its `VolumeOptions` field into a
single derived `volume_options` string that rendered as `ro`,
`<options>`, or `ro,<options>` depending on which fields were set on
the underlying attachment. That shape is fine for the legacy
`host:container[:options]` text view but it leaves drift-detection
tooling unable to tell whether a `ro` token came from
`Attachment.Readonly == true` or from the operator setting
`Attachment.VolumeOptions = "ro"` directly. The JSON now exposes
`readonly` (boolean) and `volume_options` (string) as separate
omitempty keys populated straight from the attachment, and
`formatStorageListEntry` combines them at format time for the colon-
form text view. `ParseMountPath` was extended in lockstep so callers
of the legacy `host:container:opts` form no longer have to special-
case the `ro` token themselves.
