fix(backend): drop YTM Songs filter param — it dropped the exact track

The &params= Songs-tab filter re-ranked YTM results toward a same-named
artist's discography and excluded the official track (qNffDItRUeo) entirely,
even logged-out. The default blended search (what the browser shows) ranks
the exact track first. Removing the param so yt-dlp gets the same result set.

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

backend/lib/ytdlp.js

@@ -189,10 +189,13 @@ async function downloadTrack({ jobId, artist, rawArtist, albumArtist, title, alb
     });
   });
 
-  const YTM_SONGS_PARAM = 'EgWKAQIIAWoKEAkQBRAKEAMQBA%3D%3D';
-  // Use original (raw) artist for YTM URL — better ranking since channel is in original language
+  // Use original (raw) artist for YTM URL — better ranking since channel is in original language.
+  // NOTE: do NOT append the "Songs" filter param (&params=…). The explicit Songs-tab filter
+  // re-ranks results toward a same-named artist's full discography and drops the exact track.
+  // The default blended search (what the browser shows, even logged-out) ranks the official
+  // track first — which is what we want.
   const ytmQuery = `${rawArtist || mainArtist} ${searchTitle}${albumQuerySuffix}`;
-  const ytmUrl = `https://music.youtube.com/search?q=${encodeURIComponent(ytmQuery)}&params=${YTM_SONGS_PARAM}`;
+  const ytmUrl = `https://music.youtube.com/search?q=${encodeURIComponent(ytmQuery)}`;
   const expectedAudio = path.join(dir, `${fileBase}.${CONFIG.audioFmt}`);
   const hasAudio = () => fs.existsSync(expectedAudio);