feat: server-side romaji overrides (shared list); preload ExoPlayer from SharedPreferences on cold start

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

backend/lib/config.js

@@ -1,6 +1,7 @@
 const CONFIG = {
   port:            process.env.PORT             || 3700,
   musicPath:       process.env.MUSIC_PATH       || '/music',
+  dataPath:        process.env.DATA_PATH        || '/data',
   ytdlpBin:        process.env.YTDLP_BIN       || 'yt-dlp',
   audioFmt:        process.env.AUDIO_FMT       || 'mp3',
   audioQuality:    process.env.AUDIO_QUALITY   || '0',

backend/novasonic-server.js

@@ -188,6 +188,44 @@ app.delete('/api/romaji-index', (req, res) => {
   res.json({ ok: true });
 });
 
+// ─── ROMAJI OVERRIDES (server-side, shared across all clients) ───────────────
+const _overridesFile = path.join(CONFIG.dataPath, 'romaji-overrides.json');
+
+function _loadOverrides() {
+  try { return JSON.parse(fs.readFileSync(_overridesFile, 'utf8')); } catch { return {}; }
+}
+function _saveOverrides(map) {
+  try {
+    fs.mkdirSync(CONFIG.dataPath, { recursive: true });
+    fs.writeFileSync(_overridesFile, JSON.stringify(map, null, 2), 'utf8');
+  } catch (e) { console.error('Failed to save romaji overrides:', e.message); }
+}
+
+// GET /api/romaji-overrides — returns the full kanji→romaji map
+app.get('/api/romaji-overrides', (_req, res) => res.json(_loadOverrides()));
+
+// POST /api/romaji-overrides — upsert { kanji, romaji }
+app.post('/api/romaji-overrides', (req, res) => {
+  const { kanji, romaji } = req.body;
+  if (!kanji?.trim()) return res.status(400).json({ error: 'kanji required' });
+  const map = _loadOverrides();
+  if (romaji?.trim()) map[kanji.trim()] = romaji.trim();
+  else delete map[kanji.trim()];
+  _saveOverrides(map);
+  clearRomajiCache(); // rebuild romaji index so display picks up the change
+  res.json({ ok: true });
+});
+
+// DELETE /api/romaji-overrides/:kanji — remove one entry
+app.delete('/api/romaji-overrides/:kanji', (req, res) => {
+  const kanji = decodeURIComponent(req.params.kanji);
+  const map = _loadOverrides();
+  delete map[kanji];
+  _saveOverrides(map);
+  clearRomajiCache();
+  res.json({ ok: true });
+});
+
 // POST /api/romaji-convert — convert an array of strings to romaji
 app.post('/api/romaji-convert', (req, res) => {
   const { texts } = req.body;