fix(i18n): guard locale key parity and finish the OAuth consent page strings

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.

shared/src/i18n/pl/dayplan.ts

@@ -42,5 +42,7 @@ const dayplan: TranslationStrings = {
   'dayplan.mobile.allAssigned': 'Wszystkie miejsca przypisane',
   'dayplan.mobile.noMatch': 'Brak wyników',
   'dayplan.mobile.createNew': 'Utwórz nowe miejsce',
+  'dayplan.expandAll': 'Expand all days', // en-fallback
+  'dayplan.collapseAll': 'Collapse all days', // en-fallback
 };
 export default dayplan;