Translation resources live in packages/shared/i18n/<lang>/<ns>.json
(common, errors) and ship with de and en. The web app initializes
react-i18next with bundled resources (?lng= wins, then the browser
language); all shell components use useTranslation and the temporary
t() stub is gone. The api localizes its uniform error bodies via a
minimal i18next instance negotiated from Accept-Language. `pnpm
i18n:check` fails CI when any key is missing in any language, backed
by tested helpers in @dorfteich/shared.
Closes#5
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
