Reset stops the systemd service, unmounts the overlay, and rm -rf's both
runtime/<name> and instances/<name>, but keeps the Server row, blueprint,
and (shared) systemd template. Next Start re-initializes from the current
blueprint, so users can clean up logs/caches/accumulated game state without
losing the server.
Implementation factors a shared _purge_instance helper out of
delete_instance; reset_instance reuses it without the existence guard. New
"reset" lifecycle op flows through the same route + worker + facade plumbing
as the other server ops.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
