Adds a stdlib-only Python script and a new GitHub Actions workflow
that fail any pull request which reintroduces CJK characters into
locales/en.json or which raises the total CJK match count under
backend/app or frontend/src above a committed per-path baseline.
The guard captures the two highest-signal checks of the larger
i18n-e2e-english-verification audit so it can run on every PR with a
sub-second budget and without depending on that pipeline being on
main. The committed baseline lets the codebase ratchet down toward
English-only without blocking unrelated PRs on pre-existing CJK
content; refresh it intentionally via the documented flag.
Closes#26
Dominik Seemann