CommonVolumeRadarWorker and MechanismClassifyWorker were both
returning :ok on upstream failures, so Prometheus job-failure counters
stayed at zero during multi-hour NEXRAD outages and classifier bugs
went unnoticed.
- CommonVolumeRadarWorker: distinguish permanent (4xx) from transient
errors using the same pattern as RadarFrameWorker. Permanent errors
still mark :unavailable + :ok so the backfill stops re-queueing them.
Transient errors return {:error, reason} and leave radar_status alone
so the next retry can succeed.
- MechanismClassifyWorker: keep the row-status :failed update so
operators can see which contacts blew up, but return
{:error, inspect(e)} from the rescue instead of swallowing it as :ok.
Previously the CommonVolumeRadarWorker ran silently — no URL logged,
no sign in the logs that it was doing any work. Added info-level
fetch/ok/error logs in NexradClient (same shape as WeatherFetchWorker
RAOB logs) plus start-of-work + ingestion lines in the worker itself.
Unchanged: the existing "no frame" warning and all control flow.
