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

docs/architecture.md

@@ -110,7 +110,7 @@ else a `401`.
 | `POST /api/enclosures/{id}/download`, `DELETE /api/enclosures/{id}` | `?force=true` overrides the shared-file warning |
 | `POST /api/fetch` | |
 | `GET /api/opml`, `POST /api/opml` | export your subscriptions; subscribe to every feed in an OPML |
-| `GET /api/popular`, `POST /api/popular/{id}` | what others here subscribe to (id, title, art, count; never a URL, never a private feed); subscribe by id |
+| `GET /api/popular`, `POST /api/popular/{id}` | what everyone here subscribes to, you included (id, title, art, count, whether it is yours; never a URL, never a private feed); subscribe by id |
 | `GET /api/settings`, `PATCH /api/settings` | admin-only to write |
 | `GET /api/users`, `POST /api/users`, `PATCH /api/users/{id}`, `DELETE /api/users/{id}` | admin-only; the only admin cannot be demoted or removed |
 | `GET /api/events` | SSE, the same broadcast the socket carries |