feat: Velero plugin: inspect backups and restores, trigger schedules, report storage location health

[vyrti]

PR needed?

Problem

Sofka shows Velero resources as plain objects. To find out whether last night's
backup completed, how many items it walked, or why it failed, an operator must
leave Sofka and run velero backup describe or read the object YAML. The same
is true for restores. There is also no quick way to see whether the backup
storage locations still validate, which is the first thing to check when
backups start to fail.

Proposal

One package, plugins/velero/, with three commands.

Command	Select a	Does	Changes the cluster
:velero-inspect	Backup or Restore	Shows phase, timing, item progress, errors and warnings, then the namespace lists,
validation errors and failure reason.	No
:velero-trigger	Schedule	Runs velero backup create --from-schedule.	Yes, with confirmation
:velero-locations	nothing	Reads the BackupStorageLocations and reports which ones validate.	No

:velero-inspect runs no external tool. A Velero Backup and Restore keep their
whole result in status, and Sofka already sends the selected object, so the
report comes from the request. Velero does not have to be installed on the
operator's machine for it.

:velero-locations reads the context and not a selection, so it works from any
view. It takes a namespace input that defaults to velero.

Safety

:velero-trigger is mutating and confirm. It is not marked dangerous,
because a trigger adds a backup and deletes nothing. A plugin:velero-trigger
guardrail can deny it per context or namespace, and a dry_run input shows the
command without creating anything.

Sofka matches scopes on the resource plural only, and backups, restores and
schedules are plurals other APIs also serve. Every action checks the
velero.io group, the kind, and the selected name and namespace before it
reads or changes anything. :velero-trigger accepts no replay input, because
a replayed trigger would report a backup that nothing created.

Dependencies

• velero on PATH for :velero-trigger
• kubectl on PATH for :velero-locations
• :velero-inspect needs neither

Limits

• The reports show what Velero wrote to the object. Nothing reads the backup
  tarball or the object storage.
• Per-volume snapshot and item-operation detail is not reported. Use
  velero backup describe --details for that.
• :velero-trigger does not wait for the backup, name it, or override the
  schedule's template.
• The Velero CLI publishes no Windows ARM64 binary, so :velero-trigger is
  unavailable there. The other two commands still work.

[nklmilojevic]

Feel free to add this as an issue in sofka-plugins, I accept this proposal, but as sofka-plugin, not as core.