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>

styles.css

@@ -267,8 +267,6 @@ button:focus{outline:none}
 @keyframes spin{to{transform:rotate(360deg)}}
 .player-info{min-width:0;display:flex;flex-direction:column;justify-content:center}
 .player-title{font-size:13px;font-weight:600;line-height:1.2;white-space:nowrap;overflow:hidden;text-overflow:ellipsis;transition:color .15s;margin-bottom:2px}
-/* Player bar clickable title/artist */
-.player-title:hover{color:var(--accent);text-decoration:underline}
 #player-artist-name{color:var(--accent)}
 #player-artist-name span:hover{color:var(--accent)}
 #player-album-name{color:var(--text3)}