fix: duplicate rows in artist "Top Songs" when a track exists twice in the library

Navidrome can hold the same track twice (downloaded as a single AND as an album track), so
getTopSongs returned two identical rows ("PIXELATED KISSES" x2). Collapse the top-songs list
by title+album for display (keeps the highest play count) on web + Android. SW ns-v59.

Note: this is a display fix — the underlying duplicate files remain a library-cleanup matter.

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

public/sw.js

@@ -1,4 +1,4 @@
-const CACHE = 'ns-v58';
+const CACHE = 'ns-v59';
 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.