fix(backend): use YouTube Music search URL instead of invalid ytmsearch1: prefix

ytmsearch1: is not a valid yt-dlp scheme — use full music.youtube.com URL with --playlist-items 1.

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

backend/novasonic-server.js

@@ -216,6 +216,7 @@ async function downloadTrack({ jobId, artist, albumArtist, title, album, year, t
   });
 
   const hasAudio = () => fs.readdirSync(dir).some(f => AUDIO_EXTS.some(e => f.endsWith(`.${e}`)));
+  const ytmUrl = `https://music.youtube.com/search?q=${encodeURIComponent(query)}`;
 
   if (durationMs) {
     const durationSec = Math.round(durationMs / 1000);
@@ -224,11 +225,11 @@ async function downloadTrack({ jobId, artist, albumArtist, title, album, year, t
     const durFilter = ['--match-filter', `duration > ${minDur} & duration < ${maxDur} & !is_live`];
 
     log(jobId, `🔍 Suche YT Music (~${durationSec}s): "${query}"`);
-    await spawnYtdlp([`ytmsearch1:${query}`, ...durFilter, ...baseArgs]);
+    await spawnYtdlp([ytmUrl, '--playlist-items', '1', ...durFilter, ...baseArgs]);
 
     if (!hasAudio()) {
       log(jobId, '⚠️  Kein YT-Music-Treffer im Dauerbereich — Suche ohne Filter…');
-      await spawnYtdlp([`ytmsearch1:${query}`, ...baseArgs]);
+      await spawnYtdlp([ytmUrl, '--playlist-items', '1', ...baseArgs]);
     }
     if (!hasAudio()) {
       log(jobId, '⚠️  Kein YT-Music-Treffer — Fallback zu YouTube…');
@@ -240,7 +241,7 @@ async function downloadTrack({ jobId, artist, albumArtist, title, album, year, t
     }
   } else {
     log(jobId, `🔍 Suche YT Music: "${query}"`);
-    await spawnYtdlp([`ytmsearch1:${query}`, ...baseArgs]);
+    await spawnYtdlp([ytmUrl, '--playlist-items', '1', ...baseArgs]);
 
     if (!hasAudio()) {
       log(jobId, '⚠️  Kein YT-Music-Treffer — Fallback zu YouTube…');