Every non-en locale now exposes the exact same flat key set as en. Keys that
had drifted out of sync are backfilled with the English source value (tagged
en-fallback) so t() resolves a real string instead of relying on the silent
runtime fallback; no existing translation was touched and no key was removed.
Add a parity test that imports each aggregated locale bundle and asserts its
key set matches en, with a diagnostic listing of any missing/extra keys. This
complements the file-level check in shared/scripts by guarding the merged
export the app actually serves.
Finish internationalising OAuthAuthorizePage: the ~15 remaining hardcoded
English chrome strings now go through oauth.authorize.* keys (English source
in en, en-fallback placeholders elsewhere). Markup and behaviour are unchanged.
Maurice