Add registratie wizard, BFF dashboard-view, contracts/value-objects, and architecture docs

Checkpoint of in-progress work: the registration wizard (address prefill,
DUO diploma lookup, policy questions), decision-DTO contracts, parse-don't-
validate value objects, infrastructure adapters, plus CLAUDE.md and the
architecture/ADR docs.

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

src/app/shared/ui/radio-group/radio-group.component.ts

@@ -10,10 +10,23 @@ export interface RadioOption {
     form control so it works with ngModel just like the text-input atom. */
 @Component({
   selector: 'app-radio-group',
+  styles: [`
+    .rhc-radio-option {
+      display: flex;
+      align-items: center;
+      gap: var(--rhc-space-max-md);
+      padding-block: var(--rhc-space-max-sm);
+    }
+  `],
   template: `
-    <div class="utrecht-form-field-radio-group" role="radiogroup">
+    <div
+      class="utrecht-form-field-radio-group"
+      role="radiogroup"
+      [attr.aria-labelledby]="name() + '-label'"
+      [attr.aria-invalid]="invalid() ? 'true' : null"
+      [attr.aria-describedby]="invalid() ? name() + '-error' : null">
       @for (opt of options(); track opt.value) {
-        <label class="utrecht-form-label utrecht-form-label--radio-button" style="display:flex;align-items:center;gap:0.5rem;padding:0.25rem 0">
+        <label class="utrecht-form-label utrecht-form-label--radio-button rhc-radio-option">
           <input
             class="utrecht-radio-button"
             [class.utrecht-radio-button--checked]="value === opt.value"
@@ -34,6 +47,7 @@ export interface RadioOption {
 export class RadioGroupComponent implements ControlValueAccessor {
   options = input.required<RadioOption[]>();
   name = input.required<string>();
+  invalid = input(false);
 
   value = '';
   disabled = false;