- CronJob model gains optional monitor_script/monitor_url (additive-safe)
- Job editor: Monitor mode section (off/script/url) with XOR source clearing;
disabled while no-agent is set (backend invariant); new jobs apply monitor
via create -> follow-up PUT with rollback delete on failure (the REST create
model drops the fields)
- Job list/details: blocked_config renders as a distinct error badge
('Blocked (config)'), no_change as informational; monitor source shown in
run details
Co-authored-by: M57 <hy4ri@users.noreply.github.com>