fix(spotify): parse flat title/subtitle embed format for playlist tracks

Spotify's playlist embed uses {title, subtitle, audioPreview} per track
instead of {name, artists, album}. Fixes:
- _spTrackItem: reads title as trackName, subtitle as artistName fallback,
  audioPreview.url as previewUrl, isExplicit as boolean
- Route: reads entity.authors[0].name for playlist owner, entity.subtitle
  for track artist fallback, entity.title fallback for entity.name
- Playlist tracks get playlist cover art as default artwork (no per-track art)
- Removes temporary debug logging

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

backend/novasonic-server.js

@@ -447,24 +447,38 @@ function _spArtistName(artistsRaw) {
 }
 
 function _spTrackItem(t, defaultAlbum, defaultArt, defaultAlbumArtist) {
-  // Unwrap optional {track: ...} wrapper (playlist item format)
+  // Unwrap optional {track: ...} wrapper (old playlist format)
   let raw = t?.track || t;
-  // Handle GraphQL-style {data: {__typename, name, artists, ...}}
+  // Handle GraphQL-style {data: {__typename, ...}}
   const d = raw?.data || raw;
-  const artist = _spAllArtists(d?.artists) || defaultAlbumArtist || '';
+
+  // Name: new embed uses "title", old/track embed uses "name"
+  const trackName = d?.name || d?.title || '';
+
+  // Artists: array format [{name}] or [{profile:{name}}], GraphQL {items:[...]},
+  // or flat string in "subtitle" (new playlist embed: "Myrne, Aviella")
+  let artist = '';
+  if (d?.artists) {
+    artist = _spAllArtists(d.artists);
+  } else if (typeof d?.subtitle === 'string' && d.subtitle) {
+    artist = d.subtitle;
+  }
+  artist = artist || defaultAlbumArtist || '';
+
   const art = _spArtwork(d) || defaultArt || '';
   const albumObj = d?.albumOfTrack || d?.album || {};
   const album = albumObj?.name || defaultAlbum || '';
   const date  = albumObj?.date?.isoString || albumObj?.release_date || '';
+
   return {
-    trackName:         d?.name || '',
+    trackName,
     artistName:        artist,
     collectionName:    album,
     artworkUrl100:     art,
     releaseDate:       date,
     trackNumber:       d?.trackNumber || d?.track_number,
-    trackExplicitness: d?.contentRating?.label === 'EXPLICIT' || d?.explicit ? 'explicit' : 'notExplicit',
-    previewUrl:        d?.previewUrl || d?.preview_url || null,
+    trackExplicitness: d?.contentRating?.label === 'EXPLICIT' || d?.isExplicit || d?.explicit ? 'explicit' : 'notExplicit',
+    previewUrl:        d?.previewUrl || d?.preview_url || d?.audioPreview?.url || null,
   };
 }
 
@@ -480,13 +494,14 @@ app.post('/api/spotify/resolve', async (req, res) => {
   try {
     const { type, id } = parseSpotifyUrl(url);
     const entity = await fetchSpotifyEmbed(type, id);
-    const artist = _spArtistName(entity.artists);
+    // "subtitle" is used by the flat embed format as artist/owner string
+    const artist = _spArtistName(entity.artists) || (typeof entity.subtitle === 'string' ? entity.subtitle : '');
     const artUrl = _spArtwork(entity);
 
     if (type === 'track') {
       return res.json({
         type: 'track',
-        name: entity.name,
+        name: entity.name || entity.title || '',
         artist,
         artworkUrl: artUrl,
         tracks: [_spTrackItem(entity, entity.album?.name, artUrl, artist)],
@@ -497,27 +512,28 @@ app.post('/api/spotify/resolve', async (req, res) => {
       const trackList = entity.trackList || entity.tracks?.items || [];
       return res.json({
         type: 'album',
-        name: entity.name,
+        name: entity.name || entity.title || '',
         artist,
         artworkUrl: artUrl,
-        tracks: trackList.map(t => _spTrackItem(t, entity.name, artUrl, artist)),
+        tracks: trackList.map(t => _spTrackItem(t, entity.name || entity.title, artUrl, artist)),
       });
     }
 
     if (type === 'playlist') {
       const trackList = entity.trackList || entity.content?.items || entity.tracks?.items || [];
-      const owner = entity.ownerV2?.data?.name || entity.owner?.displayName || entity.owner?.display_name || '';
-      const firstRaw = trackList[0];
-      console.log('[spotify/resolve] entity keys:', Object.keys(entity));
-      console.log('[spotify/resolve] trackList[0]:', JSON.stringify(firstRaw, null, 2).slice(0, 800));
+      const owner = entity.authors?.[0]?.name
+                 || entity.ownerV2?.data?.name
+                 || entity.owner?.displayName
+                 || entity.owner?.display_name
+                 || (typeof entity.subtitle === 'string' ? entity.subtitle : '');
       return res.json({
         type: 'playlist',
-        name: entity.name,
+        name: entity.name || entity.title || '',
         artist: owner,
         artworkUrl: artUrl,
         description: entity.description || '',
-        tracks: trackList.map(t => _spTrackItem(t, null, null, null)),
-        _debug: { entityKeys: Object.keys(entity), firstTrack: firstRaw },
+        // pass artUrl as defaultArt so tracks show the playlist cover when no per-track art exists
+        tracks: trackList.map(t => _spTrackItem(t, null, artUrl, null)),
       });
     }