Give Currently Listening its own place, below Popular

It was a section at the bottom of the Popular page, so finding the
episode you were halfway through meant opening a list of feeds first.
It is a place in the feed list now, between Popular and All
Subscriptions, with its own page and count.

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

CHANGELOG.md

@@ -20,6 +20,8 @@ The long form, with what was wrong before and how it was found, is in
 
 - 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.
+- Currently Listening is its own place in the feed list, below Popular, instead of a section at
+  the bottom of the Popular page.
 - 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.