Record an episode that turns out to be a torrent, and run it off the worker (#155)

An enclosure advertised as audio whose body is a .torrent was handed to torrent_one from inside
fetch_one, which returned without mark_downloaded, and in a scan nothing else recorded it. It
stayed pending: the page never showed it downloaded, and every scan of its feed fetched the
.torrent again and ran the torrent again, on the worker, for up to the stall limit and then the
seeding time (30 and 60 minutes in production), with no other feed checked meanwhile.

It now goes the way an advertised torrent does: in the daemon, marked downloading and handed to
spawn_torrent, which records it when it finishes; in a one-off CLI run, run there and recorded.
fetch_one answers None for the first, which a scan counts as a torrent.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

CHANGELOG.md

@@ -15,6 +15,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Fixed
 
+- An episode whose file turns out to be a torrent shows as downloaded once it is, instead of being fetched again on every check of its feed, and no longer holds up the checking of other feeds while it downloads and seeds.
 - Downloading the latest 65 to 100 items of a feed queues them at once, instead of hanging until most had downloaded and holding up adding feeds and Refresh meanwhile.
 - Changes to the feed list made at the same moment, such as two people adding feeds, or a feed added while the server settings change, no longer undo one another.
 - A download that stops partway is given up after two minutes without data, instead of holding up every scan and download until a restart.