Directory: let an admin give a blog its category

Almost no blog names a category the Directory can use, so a feed can
carry one of its own in config.toml, set by an admin in the feed's
settings and used when the feed names none. The feed's own iTunes
category still wins. The field offers the categories the Directory
already shows, so a blog about games joins Games rather than starting a
second chip. Setting it on a feed from an OPML promotes it to config, as
any other shared setting does.

Closes #10.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

CHANGELOG.md

@@ -12,6 +12,8 @@ The long form, with what was wrong before and how it was found, is in
 
 ### Added
 
+- An admin can give a feed a Directory category in its settings (`category` in config.toml), for
+  the blogs and other feeds that name none of their own. A feed's own iTunes category still wins.
 - Keyboard shortcuts after Feedly's: j and k through items, Shift-J and Shift-K through feeds,
   g and a letter to go to a place, o to play, s to pin, and more. Press ? for the whole list.
 - Directory can be filtered to Podcasts or Blogs, and by each show's own iTunes category as a row