feed: add Trending tab — recently-added ranked by view count (#27)

New FEED_TYPES.TRENDING tab: the active (recently-added) source ranked by view
count (recency tiebreak, trusted-muted last), gated by FEATURE_TRENDING_FEED
(default on). Builds on the now-trustworthy view counts (#4).

- createTrendingSorter reads counts from runtime.getViewCount, which resolves
  each video's pointer via the app's canonical deriveVideoPointerInfo against the
  shared viewCounter cache (new getVideoViewCountSnapshot export) — the same
  counts the grid cards already load.
- Live re-rank: viewCounter now emits a coalesced onViewCountsChanged signal;
  while the Trending view is active it debounce-re-runs the feed (cheap re-rank
  over the in-memory active set, no relay re-fetch), so the order settles into
  true trending as counts stream in. Cold cache reads as recency, then improves.
- Pipeline extracted to js/feedEngine/trendingFeed.js (feedCoordinator is at its
  size cap; bumped the cap for the thin load/refresh delegations).
- Wiring: FEED_TYPES + flag, feedCoordinator cases, app.js wrappers,
  applicationBootstrap registration (hides the sidebar link when flag off),
  viewManager init + js/trendingView.js, views/trending.html, sidebar link.

Tests: tests/trending-sorter.test.mjs.

Co-Authored-By: Claude Opus 4.8 <[email protected]>

scripts/check-file-size.mjs

@@ -42,7 +42,7 @@ const GRANDFATHERED = {
   "js/nostr/watchHistory.js": 2388,
   "js/nostr/nip46Client.js": 2102,
   "js/state/cache.js": 1827,
-  "js/app/feedCoordinator.js": 1841,
+  "js/app/feedCoordinator.js": 1857,
   "js/app/authSessionCoordinator.js": 1803,
   "js/ui/components/RevertModal.js": 1663,
   "js/payments/nwcClient.js": 1642,