Surface out-of-process download workers (tracked in _download_status) as
first-class tasks in /admin/api/tasks, alongside generations, training and
queued requests. They render with a percentage progress bar plus a
filename / rate / ETA readout, and can be cancelled from the Tasks page
(routed through a shared _cancel_download_session helper) or removed once
finished/failed.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>