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>

tests/page-smoke.js

@@ -88,6 +88,7 @@ const drive = [
   ['opmlModal', () => ctx.opmlModal()],
   ['selectFeed (directory)', () => ctx.selectFeed(':directory')],
   ['selectFeed (popular)', () => ctx.selectFeed(':popular')],
+  ['selectFeed (currently listening)', () => ctx.selectFeed(':listening')],
   ['selectFeed (all subscriptions)', () => ctx.selectFeed(':all')],
   ['logsModal', () => ctx.logsModal()],
   // `const S` is not reachable from here: top-level const/let do not become properties