Login screen (with a language picker), header, account menu, sync status, About and
Release Notes dialogs, and the version banner are now fully translated in Hungarian,
English and German.
Set up react-i18next with locale files auto-loaded per area (Vite glob), a compact
LanguageSwitcher, and language as a server-persisted preference (preferences.language)
mirrored to localStorage. On first login the default UI language is guessed from the
Google-reported locale (hu/en/de, else English). vite-env.d.ts types the build-time env.
