Add i18n language selector to dashboard frontend

- New i18n.js module: window.DCI18n.t(key), language dropdown selector
- Supports 5 languages (en, es, fr, de, ar) with RTL for Arabic
- Translations loaded from /api/v1/i18n/translations/:lang
- Language preference persisted in localStorage
- Added to features.js bundle

status/build.js

@@ -77,6 +77,7 @@ const bundles = {
     // window.wireModal + window.injectModal + window.escapeHtml helpers
     // defined in globals.js (already in core.js).
     JS('share-modal.js'),
+    JS('i18n.js'),
   ],
   'onboarding.js': [
     JS('driver.min.js'),