feat(design): re-theme to CIBG Huisstijl (Bootstrap 5.2), replacing RHC/Utrecht

The portal now adheres to the CIBG design system (designsystem.cibg.nl) — a customized
Bootstrap 5.2 build — replacing the Rijkshuisstijl-Community / Utrecht theme. See ADR-0003.

- Vendor @cibg/huisstijl@3.22.0 under public/cibg-huisstijl/, loaded via a <link> in
  index.html (Storybook serves it via staticDirs). Drop the two @rijkshuisstijl-community deps.
- Token bridge in styles.scss: redefine the app's ~54 --rhc-* tokens onto CIBG/--bs-* values,
  so components keep referencing tokens (no 300+ site rewrite). System-font stack; licensed
  RO/Rijks text fonts intentionally not shipped.
- Re-skin every shared atom to Bootstrap/CIBG classes (btn, form-control, form-check-*,
  table, breadcrumb, …) keeping their input() APIs. alert is hand-rolled (CIBG drops .alert);
  local .card/.badge renamed to avoid Bootstrap collisions.
- Domain pages: drop stray rhc-*/utrecht-* classes; registration-table → table table-striped.

Verified: build green, check:tokens OK, lint clean, 174 tests pass, build-storybook OK,
and the served build loads the vendored CSS (200, .btn-primary present).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/app/shared/layout/wizard-shell/wizard-shell.component.ts

@@ -35,11 +35,11 @@ export type WizardStatus = 'editing' | 'submitting' | 'submitted' | 'failed';
     @switch (status()) {
       @case ('editing') {
         <app-stepper class="app-section" [steps]="steps()" [current]="current()" />
-        <h2 #stepHeading tabindex="-1" class="rhc-heading nl-heading--level-2 app-section">{{ stepTitle() }}</h2>
+        <h2 #stepHeading tabindex="-1" class="app-section">{{ stepTitle() }}</h2>
         @if (errors().length) {
           <div #errorSummary tabindex="-1" role="alert" aria-labelledby="wizard-error-title" class="app-section">
             <app-alert type="error">
-              <h3 id="wizard-error-title" class="rhc-heading nl-heading--level-3 es-title" i18n="@@wizard.errorTitle">Er ging iets mis met uw invoer</h3>
+              <h3 id="wizard-error-title" class="es-title" i18n="@@wizard.errorTitle">Er ging iets mis met uw invoer</h3>
               <ul class="es-list">
                 @for (e of errors(); track e.id) {
                   <li><a [href]="'#' + e.id" (click)="goToField($event, e.id)">{{ e.message }}</a></li>