Downloads are now written to `filepath + '.tmp'` and atomically renamed
to the final path only on successful completion. Kiwix globs for `*.zim`
and ZimService filters `.endsWith('.zim')`, so `.tmp` files are invisible
to both during download. The same staging applies to `.pmtiles` map files.
Ref #372
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
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>
