feat: normalize Japanese artist/title names to romaji at storage time

- Add romajiForStorage() to romaji.js — smart word spacing + Title Case
- ytdlp.js: apply to folder names, filenames, and embedded tags
- novasonic-server.js: apply in edit-metadata endpoint and Spotify resolve
- spotify.js: update track artist/name from iTunes canonical English names

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

backend/novasonic-server.js

@@ -19,7 +19,7 @@ const CONFIG    = require('./lib/config');
 const { jobs, updateJob, log } = require('./lib/jobs');
 const { sanitize, lookupItunesTrackMeta, fetchItunesTracks, searchItunesAlbumTracks } = require('./lib/metadata');
 const { downloadTrack, downloadAlbumTracks } = require('./lib/downloader');
-const { buildRomajiIndex, clearRomajiCache, isTokenizerReady, fetchNdSongs } = require('./lib/romaji');
+const { buildRomajiIndex, clearRomajiCache, isTokenizerReady, fetchNdSongs, romajiForStorage } = require('./lib/romaji');
 
 // ─── INIT ─────────────────────────────────────────────────────────────────────
 const app = express();
@@ -225,6 +225,13 @@ app.post('/api/spotify/resolve', async (req, res) => {
       setTimeout(() => reject(new Error('Zeitüberschreitung — Spotify API antwortet nicht (>120s)')), 120000)
     );
     const data = await Promise.race([_resolveSpotifyViaSpotdl(url), timeout]);
+    // Normalize Japanese artist/title names to romaji before sending to frontend
+    if (data.tracks) {
+      for (const t of data.tracks) {
+        if (t.artistName) t.artistName = romajiForStorage(t.artistName) || t.artistName;
+        if (t.trackName)  t.trackName  = romajiForStorage(t.trackName)  || t.trackName;
+      }
+    }
     res.json(data);
   } catch(e) {
     console.error('[spotify/resolve]', e.message);
@@ -609,6 +616,11 @@ app.post('/api/edit-metadata', async (req, res) => {
   const normalArtist      = _normalizeArtists(artist, ';');
   const normalAlbumArtist = _normalizeArtists(albumArtist, ', ');
 
+  // Convert Japanese names to romaji for storage
+  const romajiArtist      = normalArtist      ? romajiForStorage(normalArtist)      || normalArtist      : normalArtist;
+  const romajiAlbumArtist = normalAlbumArtist ? romajiForStorage(normalAlbumArtist) || normalAlbumArtist : normalAlbumArtist;
+  const romajiTitle       = title             ? romajiForStorage(title)             || title             : title;
+
   // Resolve file path from Navidrome
   let filePath;
   let ndSong;
@@ -673,10 +685,10 @@ app.post('/api/edit-metadata', async (req, res) => {
         ffArgs.push('-map', '0:v?'); // '?' = optional, no error if file has no cover
       }
       ffArgs.push('-c', 'copy', '-map_metadata', '-1', '-id3v2_version', '3');
-      if (title)            ffArgs.push('-metadata', `title=${title}`);
-      if (normalArtist)     ffArgs.push('-metadata', `artist=${normalArtist}`);
-      const resolvedAlbumArtist = normalAlbumArtist || (normalArtist ? normalArtist.split(';')[0].trim() : null);
-      if (resolvedAlbumArtist)  ffArgs.push('-metadata', `album_artist=${resolvedAlbumArtist}`);
+      if (romajiTitle)       ffArgs.push('-metadata', `title=${romajiTitle}`);
+      if (romajiArtist)      ffArgs.push('-metadata', `artist=${romajiArtist}`);
+      const resolvedAlbumArtist = romajiAlbumArtist || (romajiArtist ? romajiArtist.split(';')[0].trim() : null);
+      if (resolvedAlbumArtist)   ffArgs.push('-metadata', `album_artist=${resolvedAlbumArtist}`);
       if (album)       ffArgs.push('-metadata', `album=${album}`);
       if (year)        ffArgs.push('-metadata', `date=${year}`);
       if (trackNum)    ffArgs.push('-metadata', `track=${totalTracks ? `${trackNum}/${totalTracks}` : String(trackNum)}`);
@@ -704,8 +716,8 @@ app.post('/api/edit-metadata', async (req, res) => {
 
     // 1. Rename file if title changed — convention: {01 - }?{Artist} - {Title}.ext
     if (title) {
-      const safeTitle      = sanitize(title);
-      const fileArtist     = (normalArtist || ndSong?.artist || '').replace(/;/g, ',');
+      const safeTitle      = sanitize(romajiTitle || title);
+      const fileArtist     = (romajiArtist || ndSong?.artist || '').replace(/;/g, ',');
       const safeArtistPart = fileArtist ? sanitize(fileArtist) + ' - ' : '';
       const prefix         = trackNum ? String(trackNum).padStart(2, '0') + ' - ' : '';
       const newName        = `${prefix}${safeArtistPart}${safeTitle}${fileExt}`;
@@ -720,7 +732,7 @@ app.post('/api/edit-metadata', async (req, res) => {
     const oldAlbumDir  = path.dirname(currentFile);
     const oldArtistDir = path.dirname(oldAlbumDir);
     const newAlbumName  = album             ? sanitize(album) : path.basename(oldAlbumDir);
-    const newArtistName = normalAlbumArtist ? sanitize(normalAlbumArtist.split(/[,;&]/)[0].trim()) : path.basename(oldArtistDir);
+    const newArtistName = romajiAlbumArtist ? sanitize(romajiAlbumArtist.split(/[,;&]/)[0].trim()) : path.basename(oldArtistDir);
     const newDir = path.join(CONFIG.musicPath, newArtistName, newAlbumName);
 
     if (newDir !== oldAlbumDir) {