List feeds in the Directory before anyone subscribes, and clear out dead ones (#107)

The Directory showed a catalogue feed only once someone subscribed, and a feed left the
catalogue with its last subscriber, so nothing could be put there for others to find.

- A feed has a listed flag, set by ipx add --list (with --category for the Directory's chip).
  The web page keeps a listed feed in the catalogue when its last subscriber leaves.
- The Directory lists every catalogue feed; Popular still only what people subscribe to.
  popular() reads titles, artwork and categories through Db::feed_list, not three queries a
  feed. Subscribing from the Directory scans the feed at once.
- A feed nobody subscribes to is checked once a day at most.
- clean_directory, in the sweep before each scan, removes from the catalogue and the database
  a feed nobody subscribes to, with no file on disk and not from an OPML, that has failed for
  30 days or published nothing in a year. Run against production first: it removes nothing.

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

CHANGELOG.md

@@ -7,6 +7,19 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Added
+
+- `ipx add --list --category News <url>` puts a feed in the Directory for anyone to subscribe to,
+  and it stays there when its last subscriber leaves.
+- Feeds nobody subscribes to that are dead for a month or quiet for a year are removed, so the
+  Directory lists feeds worth taking.
+
+### Changed
+
+- The Directory lists feeds nobody subscribes to yet; Popular still lists what people subscribe to.
+  A feed nobody subscribes to is checked once a day, and at once when someone subscribes.
+- The Directory loads faster: it asked the database three questions per feed.
+
 ## [0.9.1] - 2026-09-29
 
 ### Added