feat: romaji override list — manual kanji→romaji corrections for sort tags

Adds a maintained list in Settings where you can map kanji artist/album/title
strings to their correct romaji reading (e.g. 照井順政 → Terui Yoshimasa).
Overrides are applied last (highest priority) when the edit-metadata modal
opens, so saving the song writes the correct sort tags permanently to the file.

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

src/api.js

@@ -98,6 +98,22 @@ export async function fetchRomajiIndex() {
 
 export function invalidateRomajiIndex() { _romajiIndex = null; _romajiMap = null; _artistRomajiMap = null; }
 
+// ─── ROMAJI OVERRIDES ───
+// Manual kanji → romaji corrections stored in localStorage. Always take priority over auto-conversion.
+export function getRomajiOverrides() {
+  try { return JSON.parse(localStorage.getItem('ns_romaji_overrides') || '{}'); } catch { return {}; }
+}
+export function setRomajiOverride(kanji, romaji) {
+  const o = getRomajiOverrides();
+  if (romaji?.trim()) o[kanji.trim()] = romaji.trim(); else delete o[kanji.trim()];
+  localStorage.setItem('ns_romaji_overrides', JSON.stringify(o));
+}
+export function removeRomajiOverride(kanji) {
+  const o = getRomajiOverrides();
+  delete o[kanji];
+  localStorage.setItem('ns_romaji_overrides', JSON.stringify(o));
+}
+
 export function dispArtistById(id, name) {
   if (!S.cfg.showRomaji || !_artistRomajiMap) return name || '';
   return _artistRomajiMap.get(String(id)) || name || '';