debug: log Spotify playlist entity structure to diagnose empty tracks

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

backend/novasonic-server.js

@@ -507,6 +507,9 @@ app.post('/api/spotify/resolve', async (req, res) => {
     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));
       return res.json({
         type: 'playlist',
         name: entity.name,
@@ -514,6 +517,7 @@ app.post('/api/spotify/resolve', async (req, res) => {
         artworkUrl: artUrl,
         description: entity.description || '',
         tracks: trackList.map(t => _spTrackItem(t, null, null, null)),
+        _debug: { entityKeys: Object.keys(entity), firstTrack: firstRaw },
       });
     }