Add PurgeComponent RPC to the agent service that removes stale registry
entries for components that are both gone (observed state is removed,
unknown, or exited) and unwanted (not in any current service definition).
Refuses to purge components with running or stopped containers. When all
components of a service are purged, the service row is deleted too.
Supports --dry-run to preview without modifying the database.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>