feat: artist in filename, hide album=title subtitle, remove title hover

Naming convention (download + edit-metadata):
  Before: {01 - }Title.ext
  After:  {01 - }Artist1, Artist2 - Title.ext
- ytdlp.js: builds fileBase with artist prefix; findExistingTrack checks
  both new and old format so existing files aren't re-downloaded
- metadata.js: findExistingTrack accepts optional safeArtist param
- novasonic-server.js: file rename on title edit now includes artist
  (falls back to Navidrome's stored artist if not provided in body)

Song list subtitle: hide album name when album === title (singles where
the album is named after the track appear to duplicate the title)

Player bar: removed .player-title:hover underline/colour effect

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

backend/lib/metadata.js

@@ -47,9 +47,12 @@ async function downloadArtwork(url, dir) {
 
 const AUDIO_EXTS = ['mp3', 'flac', 'opus', 'm4a', 'ogg', 'wav'];
 
-function findExistingTrack(dir, trackPrefix, safeTitle) {
-  return AUDIO_EXTS
-    .map(ext => path.join(dir, `${trackPrefix}${safeTitle}.${ext}`))
+function findExistingTrack(dir, trackPrefix, safeTitle, safeArtist) {
+  // Check new format "{prefix}{artist} - {title}.ext" first, then old format "{prefix}{title}.ext"
+  const names = safeArtist
+    ? [`${trackPrefix}${safeArtist} - ${safeTitle}`, `${trackPrefix}${safeTitle}`]
+    : [`${trackPrefix}${safeTitle}`];
+  return AUDIO_EXTS.flatMap(ext => names.map(n => path.join(dir, `${n}.${ext}`)))
     .find(f => fs.existsSync(f)) || null;
 }