If ci-backup-template.service is killed mid-run (SIGTERM), the Python
finally block that restarts act-runner.service is skipped. A subsequent
backup then finds the runner already inactive, _stop_runner returns
False, and the finally restart is gated off — leaving the runner down
indefinitely (incident: 21 mag 2026, runner stayed off ~80 min).
Add ExecStopPost=-/bin/systemctl start act-runner.service so systemd
guarantees the runner is restarted regardless of how the unit exits
(success, failure, signal). The `-` prefix preserves the unit's own
exit status.