Popular button in the sidebar; the popular list counts everyone

- A Popular button beside + Feed opens the popular list directly; the
  Add feed dialog keeps it too.
- The list counts every subscriber, you included. Your own feeds stay on
  it, marked Subscribed, and clicking one opens it. Private feeds and
  feeds inside an OPML are still never listed, for anyone.
- GET /api/popular rows carry `subscribed`.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_016HdTEWQNrzyFULijigkmMn

tests/page-smoke.js

@@ -46,7 +46,10 @@ const ctx = {
         ? { schedule: 'every 60m', every_mins: 60, download_dir: '/tmp', max_total_gb: 0, max_age_days: 0 }
         : String(url).includes('/api/users')
           ? [{ id: 1, name: 'admin', admin: true, password: true }, { id: 2, name: 'sam', admin: false, password: false }]
-          : []),
+          : String(url).includes('/api/popular')
+            ? [{ id: 'f', title: 'A Feed', image: null, subscribers: 2, subscribed: true },
+               { id: 'g', title: null, image: null, subscribers: 1, subscribed: false }]
+            : []),
   }),
   EventSource: function () { this.close = () => {}; },
   MediaMetadata: function () {},
@@ -83,6 +86,7 @@ const drive = [
   ['prefsModal', () => ctx.prefsModal()],
   ['usersModal', () => ctx.usersModal()],
   ['opmlModal', () => ctx.opmlModal()],
+  ['showPopular', () => ctx.showPopular()],
   ['logsModal', () => ctx.logsModal()],
   // `const S` is not reachable from here: top-level const/let do not become properties
   // of a vm context the way var and function declarations do.