Sort the Directory by name either way or by subscribers (#122)

The Directory always listed A to Z, as the server sends it. A menu beside its filters now
sorts it A to Z, Z to A or by most subscribers (then by name), in the page, without asking
the server again, and the choice stays while the pane is redrawn, as the filters do. The
blurb no longer says A to Z, since it may not be.

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

CHANGELOG.md

@@ -21,6 +21,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 - The Directory browses as Apple's does: a row of categories, and once one is picked, a row of its subcategories (Tech News under News, Video Games under Leisure), instead of one row mixing both.
 - A pinned item in a list wears the same disc as a pinned feed, in the theme's accent, instead of a plain solid pin.
+- The Directory can be sorted by name, A to Z or Z to A, or by most subscribers. It still opens A to Z.
 - An item published without a title shows its opening words, in plain text rather than bold, instead of "(untitled)"; one with no text either shows its file's name, or its show and date. Opened, it starts with its text.
 - A feed that has moved for good (a permanent redirect) is followed to its new address, which iPX then reads from, and says so in the log as `feed_moved`. A temporary redirect changes nothing.
 - The daemon sleeps until the next feed is due, at most ten minutes, instead of looking every minute; refreshing or adding a feed still wakes it at once.