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/lib/romaji.js

@@ -75,6 +75,25 @@ function toRomaji(text) {
   return _hiraToRomaji(hira).toLowerCase();
 }
 
+// Human-readable romaji for storage: spaces between words, Title Case, ASCII preserved as-is.
+function romajiForStorage(text) {
+  if (!text || !_tokenizer || !JP_RE.test(text)) return text || '';
+  const tokens = _tokenizer.tokenize(text);
+  const parts = tokens.map(t => {
+    const r = t.reading;
+    if (!r || r === '*') return t.surface_form; // ASCII — keep original
+    return _hiraToRomaji(_kataToHira(r));        // Japanese — convert (lowercase)
+  });
+  // Add space between adjacent alphabetic segments (word separation for names/titles)
+  const joined = parts.reduce((acc, part, i) => {
+    if (i === 0) return part;
+    const needsSpace = /[a-zA-Z0-9]$/.test(parts[i - 1]) && /^[a-zA-Z]/.test(part);
+    return acc + (needsSpace ? ' ' : '') + part;
+  }, '');
+  // Title-case: capitalize first lowercase letter of each word, preserve existing uppercase
+  return joined.replace(/\b([a-z])/g, c => c.toUpperCase()).replace(/\s+/g, ' ').trim();
+}
+
 // ─── INDEX BUILDER ────────────────────────────────────────────────────────────
 
 const romajiCache = new Map();
@@ -123,4 +142,4 @@ function clearRomajiCache() { romajiCache.clear(); }
 
 function isTokenizerReady() { return !!_tokenizer; }
 
-module.exports = { buildRomajiIndex, clearRomajiCache, isTokenizerReady, fetchNdSongs: _fetchNdSongs };
+module.exports = { buildRomajiIndex, clearRomajiCache, isTokenizerReady, fetchNdSongs: _fetchNdSongs, romajiForStorage };

backend/lib/ytdlp.js

@@ -7,6 +7,7 @@ const {
   sanitize, navidromeArtist,
   downloadArtwork, findExistingTrack,
 } = require('./metadata');
+const { romajiForStorage } = require('./romaji');
 
 function buildTitleKeywords(title) {
   const VARIANT_WORDS = new Set(['sped','speedup','slowed','reverb','nightcore','karaoke','parody','remix','cover','acoustic','instrumental']);
@@ -49,16 +50,19 @@ function buildVariantFilter(title) {
 
 async function downloadTrack({ jobId, artist, albumArtist, title, album, year, trackNum, totalTracks, discNum, discTotal, compilation, genre, artworkUrl, explicit, outputDir, durationMs, sourceUrl }) {
   const mainArtist = albumArtist || artist;
-  const safeArtist = sanitize(mainArtist.split(/[,;&]/)[0].trim());
+  const mainArtistRomaji = romajiForStorage(mainArtist) || mainArtist;
+  const artistRomaji     = romajiForStorage(artist)     || artist;
+  const titleRomaji      = romajiForStorage(title)      || title;
+  const safeArtist = sanitize(mainArtistRomaji.split(/[,;&]/)[0].trim());
   const safeAlbum  = sanitize(album || 'Singles');
   const dir = path.join(outputDir || CONFIG.musicPath, safeArtist, safeAlbum);
   fs.mkdirSync(dir, { recursive: true });
 
-  const safeTitle        = sanitize(title);
+  const safeTitle        = sanitize(titleRomaji);
   const trackPrefix      = trackNum ? String(trackNum).padStart(2, '0') + ' - ' : '';
   // Filename format: "{01 - }Artist1, Artist2 - Title.ext"
   // Use track artist (not albumArtist) so all credited artists appear in the filename
-  const safeArtistForFile = sanitize(artist.replace(/;/g, ','));
+  const safeArtistForFile = sanitize(artistRomaji.replace(/;/g, ','));
   const fileBase          = `${trackPrefix}${safeArtistForFile} - ${safeTitle}`;
 
   const existing = findExistingTrack(dir, trackPrefix, safeTitle, safeArtistForFile);
@@ -299,13 +303,16 @@ async function embedMetadata({ jobId, audioFile, dir, trackPrefix, safeTitle, ar
     if (hasCover) ffArgs.push('-i', coverPath);
     ffArgs.push('-map', '0:a');
     if (hasCover) ffArgs.push('-map', '1:v');
+    const storedTitle       = romajiForStorage(title)                                       || title;
+    const storedArtist      = romajiForStorage(navidromeArtist(artist))                    || navidromeArtist(artist);
+    const storedAlbumArtist = romajiForStorage(mainArtist.replace(/\s+&\s+/g, ', '))       || mainArtist.replace(/\s+&\s+/g, ', ');
     ffArgs.push(
       '-c',             'copy',
       '-map_metadata',  '-1',
       '-id3v2_version', '3',
-      '-metadata', `title=${title}`,
-      '-metadata', `artist=${navidromeArtist(artist)}`,
-      '-metadata', `album_artist=${mainArtist.replace(/\s+&\s+/g, ', ')}`,
+      '-metadata', `title=${storedTitle}`,
+      '-metadata', `artist=${storedArtist}`,
+      '-metadata', `album_artist=${storedAlbumArtist}`,
     );
     if (album)       ffArgs.push('-metadata', `album=${album}`);
     if (year)        ffArgs.push('-metadata', `date=${String(year)}`);