feat(fp): WP-20 — second locale proof (nl/en build seam)

angular.json gains an i18n block (sourceLocale nl, en translation file) and
an `en` build/serve configuration with i18nMissingTranslation: "error" so a
new $localize string without an English unit fails the build, not silently
falls back. CI now runs `ng build --localize` to build both locales every
run. Verified end-to-end, not just "the build succeeded": the nl bundle
ships "Inloggen met DigiD", the en bundle ships "Log in with DigiD".

Incidental: prettier/compodoc regen noise in docs/wcag-checklist.md,
src/docs/a11y.mdx, documentation.json from the same working session.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

.github/workflows/ci.yml

@@ -30,7 +30,10 @@ jobs:
       - run: npm run format:check
       - run: npm run check:tokens
       - run: npm test
-      - run: npm run build
+      # --localize builds every configured locale (nl + en, angular.json's i18n
+      # block) in one pass; i18nMissingTranslation:"error" (angular.json) fails
+      # this step if messages.en.xlf is missing a unit the source (WP-20) gains.
+      - run: npx ng build --localize
       # The shipped bundle must stay clean; dev-only advisories are excluded.
       - run: npm audit --omit=dev