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/text-input/text-input.component.ts

@@ -10,6 +10,8 @@ import { ControlValueAccessor, NG_VALUE_ACCESSOR } from '@angular/forms';
       [class.utrecht-textbox--invalid]="invalid()"
       [type]="type()"
       [id]="inputId()"
+      [attr.aria-invalid]="invalid() ? 'true' : null"
+      [attr.aria-describedby]="invalid() && inputId() ? inputId() + '-error' : null"
       [placeholder]="placeholder()"
       [disabled]="disabled"
       [value]="value"