A scan runs on a background thread inside the API process. If that process
dies mid-scan — an OOM kill, docker stop, a crash — the ScanRun row stays
"running" for ever, because nothing is left alive to finish it.
That row is not just cosmetic clutter in Scan History: the trigger endpoints
reject a new scan while one is "running" for the same target, so a single kill
locks that range out permanently.
Nothing can legitimately be "running" the moment we boot, so lifespan() now
marks every such row "error" — the same word run_scan and run_device_scan
write when they fail themselves — with finished_at and an explanatory message.
Reported alongside the OOM itself in #374, which is what produced the orphans.
Fixes#374
ha-relevant: maybe
Pouzor
05c0da53e6