feat: romaji index for Japanese kanji song search

Backend:
- Add /api/romaji-index endpoint using kuromoji morphological analyzer
- Fetches all Navidrome songs, converts kanji → hiragana readings → romaji
- Only indexes songs with Japanese characters; caches for 20 min
- /api/romaji-index DELETE clears cache (force rebuild)

Frontend:
- fetchRomajiIndex() in api.js: lazy-fetches and caches the index
- doLocalSearch: when query is romaji (ASCII), queries romaji index in
  parallel with Navidrome search3 and merges+deduplicates results

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

src/api.js

@@ -39,6 +39,25 @@ export async function ndAuth() {
   return S._ndToken;
 }
 
+// ─── ROMAJI INDEX ───
+// Fetched once per session from the backend, cached in memory.
+let _romajiIndex = null;
+let _romajiIndexFetch = null; // in-flight promise dedup
+
+export async function fetchRomajiIndex() {
+  if (!S.cfg.backendUrl || !S.cfg.url || !S.cfg.user || !S.cfg.pass) return null;
+  if (_romajiIndex) return _romajiIndex;
+  if (_romajiIndexFetch) return _romajiIndexFetch;
+  _romajiIndexFetch = fetch(
+    `${S.cfg.backendUrl}/api/romaji-index?ndUrl=${encodeURIComponent(S.cfg.url)}&user=${encodeURIComponent(S.cfg.user)}&pass=${encodeURIComponent(S.cfg.pass)}`
+  ).then(r => r.ok ? r.json() : null)
+   .then(idx => { _romajiIndex = idx; _romajiIndexFetch = null; return idx; })
+   .catch(() => { _romajiIndexFetch = null; return null; });
+  return _romajiIndexFetch;
+}
+
+export function invalidateRomajiIndex() { _romajiIndex = null; }
+
 // ─── ITUNES ───
 // Route through backend proxy to avoid CORS; fall back to direct if no backend configured.
 function _itunesBase() {

src/views.js

@@ -6,6 +6,7 @@ import { playQueue, dlSongLocal, playPreview } from './player.js';
 import { showCtxMenu, openEditPlModal, openDlModal, closeSidebar, switchNavMode } from './ui.js';
 import { closeNowPlaying, closeNpMenu } from './nowplaying.js';
 import { makeCard, makeAlbumCard, makeSongItem, makeGlobalTrackItem, mkSection } from './components.js';
+import { fetchRomajiIndex } from './api.js';
 import { loadSpotifyImporter } from './spotify.js';
 
 // ─── NAVIGATION HISTORY ───
@@ -723,16 +724,25 @@ export async function doLocalSearch(q) {
   el.innerHTML = '<div class="spinner"></div>';
   try {
     const hiragana = await _romajiToHiragana(q);
-    const [r, r2] = await Promise.all([
+    const isRomaji = /^[a-z\s'-]+$/i.test(q.trim());
+    const [r, r2, romajiIdx] = await Promise.all([
       api('search3', `&query=${encodeURIComponent(q)}&songCount=30&albumCount=10&artistCount=6`),
       hiragana ? api('search3', `&query=${encodeURIComponent(hiragana)}&songCount=20&albumCount=6&artistCount=4`) : Promise.resolve(null),
+      isRomaji ? fetchRomajiIndex() : Promise.resolve(null),
     ]);
     const res  = r.searchResult3  || {};
     const res2 = r2?.searchResult3 || {};
     el.innerHTML = '';
     const artists = _mergeUniq(res.artist||[], res2.artist);
     const albums  = _mergeUniq(res.album ||[], res2.album);
-    const songs   = _mergeUniq(res.song  ||[], res2.song);
+
+    // Merge Navidrome results with romaji index matches
+    const qLow = q.trim().toLowerCase();
+    const romajiHits = romajiIdx
+      ? romajiIdx.filter(e => e.r.includes(qLow))
+      : [];
+    const songs = _mergeUniq(_mergeUniq(res.song||[], res2.song), romajiHits);
+
     if(!artists.length && !albums.length && !songs.length) {
       el.innerHTML = '<div class="empty-state"><div class="icon">🔍</div><p>Keine Ergebnisse</p></div>'; return;
     }