feat: load actual file sort tags in edit modal + remove settings hints

- backend: new GET /api/song-sorttags reads TITLESORT/ARTISTSORT/ALBUMARTISTSORT/
  ALBUMSORT directly from the file via ffprobe
- ui.js: pre-fill sort fields from romaji index, then overwrite with real file
  tags from the backend (shows actual values even if manually set)
- index.html: remove redundant hint texts in settings

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

backend/novasonic-server.js

@@ -612,6 +612,43 @@ app.get('/api/musicbrainz/lookup', async (req, res) => {
   }
 });
 
+// ─── SORT TAGS READ ──────────────────────────────────────────────────────────
+app.get('/api/song-sorttags', async (req, res) => {
+  const { ndUrl, user, pass, songId } = req.query;
+  if (!ndUrl || !user || !pass || !songId) return res.status(400).json({ error: 'ndUrl, user, pass, songId required' });
+  let filePath;
+  try {
+    const salt  = Math.random().toString(36).slice(2, 10);
+    const token = crypto.createHash('md5').update(pass + salt).digest('hex');
+    const ndRes = await fetch(`${ndUrl}/rest/getSong?id=${songId}&u=${encodeURIComponent(user)}&t=${token}&s=${salt}&v=1.16.1&c=novasonic&f=json`, { signal: AbortSignal.timeout(8000) });
+    const nd    = await ndRes.json();
+    filePath    = nd?.['subsonic-response']?.song?.path;
+    if (!filePath) return res.status(404).json({ error: 'Song not found' });
+  } catch (e) { return res.status(502).json({ error: e.message }); }
+  if (!path.isAbsolute(filePath)) filePath = path.join(CONFIG.musicPath, filePath);
+  if (!fs.existsSync(filePath)) {
+    const found = _findFileRecursive(CONFIG.musicPath, path.basename(filePath));
+    if (found) filePath = found; else return res.status(404).json({ error: 'File not found' });
+  }
+  try {
+    const out = await new Promise((resolve, reject) => {
+      const proc = spawn('ffprobe', ['-v', 'quiet', '-print_format', 'json', '-show_entries', 'format_tags', filePath]);
+      let buf = '';
+      proc.stdout.on('data', d => buf += d);
+      proc.on('error', reject);
+      proc.on('close', () => { try { resolve(JSON.parse(buf)); } catch { resolve({}); } });
+    });
+    const tags = out?.format?.tags || {};
+    const findTag = (...keys) => { for (const k of keys) { const v = tags[k] || tags[k.toLowerCase()] || tags[k.toUpperCase()]; if (v) return v; } return ''; };
+    res.json({
+      titleSort:        findTag('TITLESORT', 'titlesort'),
+      artistSort:       findTag('ARTISTSORT', 'artistsort'),
+      albumArtistSort:  findTag('ALBUMARTISTSORT', 'albumartistsort', 'TSO2'),
+      albumSort:        findTag('ALBUMSORT', 'albumsort'),
+    });
+  } catch (e) { res.status(500).json({ error: e.message }); }
+});
+
 // ─── METADATA EDIT ───────────────────────────────────────────────────────────
 app.post('/api/edit-metadata', async (req, res) => {
   const { ndUrl, user, pass, songId, title, artist, albumArtist, album, year, trackNum, totalTracks,