Three bugs caused downloads to hang, disappear, or leave stuck spinners:
1. Wikipedia downloads that failed never updated the DB status from 'downloading',
leaving the spinner stuck forever. Now the worker's failed handler marks them as failed.
2. No stall detection on streaming downloads - if data stopped flowing mid-download,
the job hung indefinitely. Added a 5-minute stall timer that triggers retry.
3. Failed jobs were invisible to users since only waiting/active/delayed states were
queried. Now failed jobs appear with error indicators in the download list.
Closes#364, closes#216
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
