feat(scrobble): Android stats screen + cover art in stats (web + android)

Phase 4 (part B): Android statistics screen consuming GET /scrobble/stats —
tiles (plays + listening time), day/month/year play series, top artists/tracks/
albums, 24h listening clock, period tabs; opened from a Settings button
("Meine Statistiken"). New StatsViewModel + StatsScreen + ScrobbleModels;
PlayLogClient.fetchStats() (tolerant JSON decode, null on any failure);
repo.fetchScrobbleStats(); nav route + SettingsScreen(onOpenStats).

Cover art everywhere: top artists show a circular artist image, tracks/albums
a square cover — resolved client-side from Navidrome via artistId/albumId/songId
(no coverArt knowledge in the scrobble service). Endpoint now also returns
albumId for top tracks so track covers resolve reliably. Web stats list gets the
same thumbnails. SW cache -> ns-v67.

Android compileDebugKotlin + web build green. Needs on-device runtime test.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

public/sw.js

@@ -1,4 +1,4 @@
-const CACHE = 'ns-v66';
+const CACHE = 'ns-v67';
 const PRECACHE = ['/', 'index.html', 'manifest.json', 'icon.svg'];
 const SKIP_PATHS = ['/rest/stream', '/rest/download', '/config.js'];
 // Auth token params stripped from cache keys so artwork survives across sessions/token refreshes.