test(portal-openbaar): drive the openbaar register page — list, search, empty state (refs #10)

Scaffolds the anonymous openbaar Angular app (mirrors self-service: standalone +
signals, NL DS via the ui lib, no auth) and adds a failing register-page spec:
loads the public register from the BFF on open, searches by term, and shows an
empty-state message. The stub page renders only the heading, so the list/search/
empty-state assertions fail (red).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

apps/openbaar/src/styles.css

@@ -0,0 +1,2 @@
+/* NL Design System theme — Utrecht design tokens (docs/frontend-decisions.md). */
+@import '@utrecht/design-tokens/dist/index.css';