Adds optional live status checking per service (not just per node),
requested as a follow-up to issue #196.
Backend:
- New check_service / check_services: HTTP(S) GET for web services, TCP
connect otherwise; UDP and port-less non-web services stay 'unknown'.
- New scheduler job 'service_checks', independent interval (default 300s),
added/removed live via set_service_checks_enabled.
- Settings gain service_check_enabled + service_check_interval (>=30s),
persisted to scan_config.json. New WS message type 'service_status'.
Frontend:
- Live per-service status overlay in canvasStore (not persisted, so it
never round-trips through canvas save), fed by the WS message.
- DetailPanel + canvas node service rows: offline service turns red
(#f85149), otherwise keeps its category colour.
- SettingsModal: toggle + interval input (default 300s / 5 min).
Off by default — no behaviour change until enabled.
ha-relevant: yes
Pouzor
bcc488993d