Add FireflyGo sync mode, extra_data controls and Enka import

- js/modes.js: per-backend capability matrix (GaCy GO / FireflyGo / RobinSR)
- js/firefly.js: POST /sync payload builder + extra_data normaliser
- js/enka-import.js: enka.network -> FreeSR converter with merge/replace
- app.js: mode-aware UI, firefly transport, Enka import, extra_data form
- index.html: enable FireflyGo, add Enka import + FireflyGo controls cards
- i18n: Thai/English strings for every new label, message and error
- vercel.json: /api/enka/:uid rewrite; scripts/dev-server.cjs for local dev

js/item-catalog.js

@@ -1,4 +1,4 @@
-import { getCurrentLanguage, t, translatePath } from './i18n.js?v=2.22';
+import { getCurrentLanguage, t, translatePath } from './i18n.js?v=2.23';
 
 const CATALOG_URL = new URL('../assets/item-catalog.json?v=2', import.meta.url);
 const PAGE_SIZE = 48;