frontend-i18n

Internationalization for the RomM frontend (both v1 and v2). Use whenever adding, renaming, or removing any user-visible string / translation key under frontend/src/locales/. Covers the en_US-is-source rule, the requirement to add every new key to ALL locale directories in the same change, namespace layout, and the check_i18n_locales.py validator enforced in CI. Trigger on any change to frontend/src/locales/.