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>

src/docs/a11y.mdx

@@ -47,7 +47,7 @@ screen reader announces the hint, then the error, never neither. See
 <Canvas of={AlertStories.Error} />
 
 Errors are `role="alert"` (assertive — interrupts, because the user needs to know
-*now*); info/ok/warning stay `role="status"` (polite) so they don't interrupt whatever
+_now_); info/ok/warning stay `role="status"` (polite) so they don't interrupt whatever
 the user is doing. See `alert.component.ts`.
 
 ## Route-change focus
@@ -64,6 +64,6 @@ the same way (`withInMemoryScrolling`), both wired once in `app.config.ts` — n
 `npm run lint` fails the build on a real template a11y violation, and `test-storybook:ci`
 fails it on a real axe violation. Both can be locally disabled — the lint rule via a
 normal ESLint disable comment, axe via `parameters: { a11y: { disable: true } }` — but
-only with a comment naming *why* and a cross-reference to the WP expected to remove the
+only with a comment naming _why_ and a cross-reference to the WP expected to remove the
 skip (see `docs/backlog/WP-13-cibg-gap-register.md`'s marker convention, reused here).
 Grep `a11y: { disable: true }` in `*.stories.ts` for the current list.