Leave a removed account's feeds as unsubscribing does (#157)

Removing an account deleted the user, and the foreign keys took their subscriptions with them, but
nothing did what unsubscribing does next: a feed nobody subscribes to any more leaves the catalogue
(or stays, if listed, for the Directory). A feed only that person read stayed with no subscribers,
and a feed with none downloads by its own settings, so it went on fetching each new episode, daily,
for no one, until it had been quiet for a year.

remove_feed's body is now leave(), and remove_user() leaves each of the person's feeds with it before
deleting the account, from the page and from `ipx user rm` alike; a feed inside a group of theirs
goes with the group. `ipx user rm` now tells a running daemon to reload, as add and rm do (#120),
since it can change the catalogue.

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
 
+- Removing an account takes the feeds only that person read off the server, as unsubscribing does, instead of leaving them downloading every new episode for no one.
 - Freeing disk space counts only the people who subscribe to a feed: an episode is no longer taken as heard by everyone because someone who has since unsubscribed heard it, and their pins no longer keep files for good.
 - 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.