feat: sort genre pills by total play count via backend

Page loads instantly with song-count order, then silently re-sorts
once the backend aggregates play counts across all songs. Result cached
20 min server-side to avoid repeated full-library fetches.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/views.js

@@ -182,6 +182,17 @@ async function loadGenreSection() {
     _renderGenres();
     if (_allGenres.length > GENRE_LIMIT() && more) more.style.display = '';
   } catch { el.style.display = 'none'; }
+  // Re-sort by total play count once backend data arrives (non-blocking)
+  if (S.cfg.backendUrl && _allGenres.length) {
+    fetch(`${S.cfg.backendUrl}/api/genre-playcounts?ndUrl=${encodeURIComponent(S.cfg.url)}&user=${encodeURIComponent(S.cfg.user)}&pass=${encodeURIComponent(S.cfg.pass)}`)
+      .then(r => r.ok ? r.json() : null)
+      .then(plays => {
+        if (!plays || !_allGenres.length) return;
+        _allGenres.sort((a, b) => (plays[b.value] || 0) - (plays[a.value] || 0));
+        _renderGenres();
+      })
+      .catch(() => {});
+  }
 }
 
 function _renderGenres() {