feat(portal-self-service): implement the DigiD registration submit page (refs #67)

RegistrationPage shows the signed-in BSN and submits to the BFF via the generated
api-client, confirming with the returned reference; built from NL Design System
(Utrecht) components. Wire the guarded route + app providers (DigiD OIDC + token
interceptor + HttpClient), the NL DS theme, and lang=nl. Component tests
(Testing Library) + axe (WCAG 2.1 AA) pass; a guard test covers libs/auth. Replace
the demo eslint depConstraints (scope:shop/shared) with a permissive default.

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

libs/ui/src/index.ts

@@ -1,10 +1,17 @@
 // NL Design System building blocks — Utrecht is NL DS's reference Angular implementation
 // (docs/frontend-decisions.md). The portals depend on the design system through this one lib.
 // The design tokens/theme CSS is imported once, at the app level (apps/*/src/styles.css).
+//
+// The Utrecht v3 components are NgModule-based (not standalone), so we re-export the module.
+// A standalone component consumes them by importing UtrechtComponentsModule in its `imports`
+// (CLAUDE.md §10 forbids *declaring* NgModules in our code, not consuming a third-party one).
+// The component classes are re-exported too so the AOT compiler can resolve the template
+// directives (utrecht-article, utrecht-button, …) through this barrel.
 export {
   UtrechtArticle,
   UtrechtButtonAttr,
+  UtrechtComponentsModule,
   UtrechtDocument,
-  UtrechtHeading,
+  UtrechtHeading1,
   UtrechtParagraph,
 } from '@utrecht/component-library-angular';