Directory: chips by kind and category over a grid of cover art

Feeds take their channel's first <itunes:category> into a new feeds.category
column; the migration drops ETag and Last-Modified once so every feed re-reads
on its normal schedule and picks one up. /api/popular and /api/directory carry
category and podcast (any audio or video enclosure). Directory becomes a grid of
cover-art tiles under a chip rail: All, Podcasts, Blogs, and a podcast's
categories once Podcasts is picked. Popular and Add a feed keep their rows.

Closes #4, closes #5, closes #6, closes #7.

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

CHANGELOG.md

@@ -10,6 +10,18 @@ The long form, with what was wrong before and how it was found, is in
 
 ## [Unreleased]
 
+### Added
+
+- Directory has a row of chips above it: Podcasts, Blogs, and once Podcasts is picked, each
+  podcast's own iTunes category. Picking one filters the Directory in place.
+
+### Changed
+
+- Directory shows each feed as its cover art in a grid, title and subscriber count underneath,
+  instead of a list. Popular and the Add a feed dialog keep their rows.
+- The first scan after upgrading fetches every feed in full once, on its usual schedule, so each
+  picks up its category without waiting for the publisher to change something.
+
 ## [0.5.5] - 2026-09-14
 
 ### Changed