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.
About (in the account menu) shows frontend/backend/database versions + build.
Release Notes renders per-version highlights with a commit-SHA reference; a
dismissible banner appears once after the running build's version changes and
links into the notes. Adds a reusable Modal shell and the release-notes data
(detailed v0.1.0).