fix: album/artist download now saves individual tracks with full metadata

- Remove broken 'full album' fallback that downloaded everything as one MP3
- Add searchItunesAlbumTracks() so albums without a collectionId can still
  be resolved to individual tracks via iTunes search
- Prefix filenames with zero-padded track number (01 - Title.mp3)
- Write track tag as 'N/total' format (e.g. 3/12) plus totaltracks tag
  so Navidrome gets correct track order and total count

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

backend/novasonic-server.js

@@ -80,14 +80,15 @@ function log(jobId, msg) {
 // We do NOT use --postprocessor-args for metadata because yt-dlp splits that string on
 // spaces internally, so any metadata value with a space (e.g. album name) gets corrupted.
 // Instead: yt-dlp downloads, then we call ffmpeg ourselves with properly separated args.
-async function downloadTrack({ jobId, artist, title, album, year, trackNum, artworkUrl, outputDir }) {
+async function downloadTrack({ jobId, artist, title, album, year, trackNum, totalTracks, artworkUrl, outputDir }) {
   const safeArtist = sanitize(artist);
   const safeAlbum  = sanitize(album || 'Singles');
   const dir = path.join(outputDir || CONFIG.musicPath, safeArtist, safeAlbum);
   fs.mkdirSync(dir, { recursive: true });
 
   const safeTitle      = sanitize(title);
-  const outputTemplate = path.join(dir, `${safeTitle}.%(ext)s`);
+  const trackPrefix    = trackNum ? String(trackNum).padStart(2, '0') + ' - ' : '';
+  const outputTemplate = path.join(dir, `${trackPrefix}${safeTitle}.%(ext)s`);
   const query          = `${artist} - ${title} official audio`;
   log(jobId, `\uD83D\uDD0D Suche: "${query}"`);
 
@@ -155,9 +156,10 @@ async function downloadTrack({ jobId, artist, title, album, year, trackNum, artw
       '-metadata', `artist=${artist}`,
       '-metadata', `album_artist=${artist}`,
     ];
-    if (album)    ffArgs.push('-metadata', `album=${album}`);
-    if (year)     ffArgs.push('-metadata', `date=${String(year)}`);
-    if (trackNum) ffArgs.push('-metadata', `track=${String(trackNum)}`);
+    if (album)       ffArgs.push('-metadata', `album=${album}`);
+    if (year)        ffArgs.push('-metadata', `date=${String(year)}`);
+    if (trackNum)    ffArgs.push('-metadata', `track=${totalTracks ? `${trackNum}/${totalTracks}` : String(trackNum)}`);
+    if (totalTracks) ffArgs.push('-metadata', `totaltracks=${String(totalTracks)}`);
     ffArgs.push(tmpFile, '-y');
 
     const ff = spawn('ffmpeg', ffArgs);
@@ -224,13 +226,14 @@ async function downloadAlbumTracks({ jobId, artist, albumTitle, tracks, artworkU
     try {
       await downloadTrack({
         jobId,
-        artist:   track.artistName   || artist,
-        title:    track.trackName    || track.title,
-        album:    albumTitle,
-        year:     track.releaseDate  ? new Date(track.releaseDate).getFullYear() : undefined,
-        trackNum: track.trackNumber  || undefined,
-        artworkUrl: artworkUrl || track.artworkUrl100,
-        outputDir: CONFIG.musicPath,
+        artist:      track.artistName  || artist,
+        title:       track.trackName   || track.title,
+        album:       albumTitle,
+        year:        track.releaseDate ? new Date(track.releaseDate).getFullYear() : undefined,
+        trackNum:    track.trackNumber || undefined,
+        totalTracks: total,
+        artworkUrl:  artworkUrl || track.artworkUrl100,
+        outputDir:   CONFIG.musicPath,
       });
       done++;
       updateJob(jobId, { progress: Math.round((done / total) * 90) });
@@ -240,6 +243,28 @@ async function downloadAlbumTracks({ jobId, artist, albumTitle, tracks, artworkU
   }
 }
 
+// Search iTunes for an album by artist+name and return its tracks
+async function searchItunesAlbumTracks(artist, album) {
+  return new Promise(resolve => {
+    const q = encodeURIComponent(`${artist} ${album}`);
+    https.get(`https://itunes.apple.com/search?term=${q}&media=music&entity=album&limit=5&country=de`, res => {
+      let d = '';
+      res.on('data', c => d += c);
+      res.on('end', () => {
+        try {
+          const results = JSON.parse(d).results || [];
+          const match = results.find(r =>
+            r.collectionName?.toLowerCase().includes(album.toLowerCase()) ||
+            r.artistName?.toLowerCase().includes(artist.toLowerCase())
+          );
+          if (match) fetchItunesTracks(match.collectionId).then(resolve).catch(() => resolve([]));
+          else resolve([]);
+        } catch { resolve([]); }
+      });
+    }).on('error', () => resolve([]));
+  });
+}
+
 // Fetch iTunes album tracks
 async function fetchItunesTracks(collectionId) {
   return new Promise((resolve, reject) => {
@@ -331,12 +356,14 @@ app.post('/api/download', async (req, res) => {
           log(jobId, '📋 Lade Track-Liste von iTunes…');
           tracks = await fetchItunesTracks(collectionId);
         }
-        if (tracks.length) {
-          await downloadAlbumTracks({ jobId, artist, albumTitle: album || title, tracks, artworkUrl });
-        } else {
-          // Fallback: download full album search
-          await downloadTrack({ jobId, artist, title: `${album || title} full album`, album, artworkUrl });
+        if (!tracks.length) {
+          log(jobId, '🔍 Suche Album auf iTunes…');
+          tracks = await searchItunesAlbumTracks(artist, album || title);
         }
+        if (!tracks.length) {
+          throw new Error(`Keine einzelnen Tracks für "${album || title}" gefunden. Bitte über die iTunes Global-Suche herunterladen.`);
+        }
+        await downloadAlbumTracks({ jobId, artist, albumTitle: album || title, tracks, artworkUrl });
         updateJob(jobId, { status: 'done', progress: 100, message: `Album "${album || title}" fertig!` });
 
       } else if (type === 'artist') {