fix: expose attachment readonly and volume_options in storage:list json

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.

plugins/storage/migrate.go

@@ -174,13 +174,8 @@ func migrateMount(appName string, mount string, phases []string) error {
 		ContainerPath: containerPath,
 		Phases:        phases,
 		ProcessType:   DefaultProcessType,
-	}
-	if parsed.VolumeOptions != "" {
-		if parsed.VolumeOptions == "ro" {
-			attachment.Readonly = true
-		} else {
-			attachment.VolumeOptions = parsed.VolumeOptions
-		}
+		Readonly:      parsed.Readonly,
+		VolumeOptions: parsed.VolumeOptions,
 	}
 
 	existing, err := LoadAttachments(appName)