feat(most-played): add dedicated Most Played page (#86)

New sidebar item (TrendingUp icon, /most-played route) with:

- Top Artists section: derived by grouping frequent albums by artistId
  and summing playCount — no extra API calls needed. Shows up to 10
  artists as a responsive grid with avatar, rank and total play count.
- Top Albums section: paginated list using getAlbumList('frequent'),
  50 albums per batch with a "Load more" button. Each row shows rank,
  cover thumbnail (44px), album name, artist (navigates to artist
  page), year and play count.
- Sort toggle (most plays first / fewest plays first).

Also adds playCount?: number to SubsonicAlbum — Navidrome returns this
field in getAlbumList2?type=frequent but it was missing from the type.

Closes #86

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

src/App.tsx

@@ -26,6 +26,7 @@ import Login from './pages/Login';
 import AlbumDetail from './pages/AlbumDetail';
 import LabelAlbums from './pages/LabelAlbums';
 import Statistics from './pages/Statistics';
+import MostPlayed from './pages/MostPlayed';
 import Help from './pages/Help';
 import RandomAlbums from './pages/RandomAlbums';
 import SearchResults from './pages/SearchResults';
@@ -304,6 +305,7 @@ function AppShell() {
             <Route path="/search" element={<SearchResults />} />
             <Route path="/search/advanced" element={<AdvancedSearch />} />
             <Route path="/statistics" element={<Statistics />} />
+            <Route path="/most-played" element={<MostPlayed />} />
             <Route path="/now-playing" element={isMobile ? <MobilePlayerView /> : <NowPlayingPage />} />
             <Route path="/settings" element={<Settings />} />
             <Route path="/help" element={<Help />} />