fix: fetch romaji index on startup when showRomaji is enabled

On page reload the saved cfg restored showRomaji=true but _romajiMap was
never fetched, so all display helpers fell back to Japanese text. Await
fetchRomajiIndex before the first navigate when the setting is on.

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

src/main.js

@@ -1,6 +1,6 @@
 import { S } from './state.js';
 import { toast } from './utils.js';
-import { api } from './api.js';
+import { api, fetchRomajiIndex } from './api.js';
 import { injectPWA } from './pwa.js';
 import { loadSavedTheme } from './themes.js';
 import {
@@ -94,6 +94,7 @@ async function startApp() {
     if (bnav) bnav.style.display = '';
     absLoadSettingsLibraries();
   }
+  if (S.cfg.showRomaji) await fetchRomajiIndex().catch(() => {});
   if(_navLoad() && S._navCursor >= 0 && S._navStack[S._navCursor]) {
     const last = S._navStack[S._navCursor];
     S._navJumping = true;