feat(portal-frontend): implement edit-applicant-details form with write-through disclaimer

Shared form for writeThrough and owned modes. Shows the ADR-002
disclaimer only in writeThrough mode (no client-side validation
stricter than legacy provides). Maps 400 ErrorsResponse to per-field
inline errors, 422/409 to a banner with the server's own text -
never a client-side switch over invariant names. Embedded in
case-detail with reload() on save so the actions block refreshes.

portal-frontend/src/app/case-detail/edit-applicant-details/edit-applicant-details.html

@@ -0,0 +1,73 @@
+<form (ngSubmit)="submit()">
+  @if (isWriteThrough) {
+    <p class="disclaimer" data-testid="write-through-disclaimer">
+      Gevalideerd door het legacy systeem — Angular voegt hier geen eigen validatie toe.
+    </p>
+  }
+
+  @if (banner) {
+    <p class="banner" data-testid="edit-details-banner">{{ banner }}</p>
+  }
+
+  <label>
+    Achternaam
+    <input type="text" name="surname" required [(ngModel)]="surname" />
+  </label>
+  @if (fieldErrors['surname']; as error) {
+    <p class="field-error" data-testid="field-error-surname">{{ error }}</p>
+  }
+
+  <label>
+    Voorletters
+    <input type="text" name="initials" required [(ngModel)]="initials" />
+  </label>
+
+  <label>
+    Straat
+    <input type="text" name="street" [(ngModel)]="street" />
+  </label>
+
+  <label>
+    Huisnummer
+    <input type="text" name="number" [(ngModel)]="number" />
+  </label>
+  @if (fieldErrors['address.number']; as error) {
+    <p class="field-error" data-testid="field-error-address.number">{{ error }}</p>
+  }
+
+  <label>
+    Postcode
+    <input type="text" name="postalCode" [(ngModel)]="postalCode" />
+  </label>
+  @if (fieldErrors['address.postalCode']; as error) {
+    <p class="field-error" data-testid="field-error-address.postalCode">{{ error }}</p>
+  }
+
+  <label>
+    Plaats
+    <input type="text" name="city" [(ngModel)]="city" />
+  </label>
+
+  <label>
+    E-mail
+    <input type="email" name="email" [(ngModel)]="email" />
+  </label>
+  @if (fieldErrors['email']; as error) {
+    <p class="field-error" data-testid="field-error-email">{{ error }}</p>
+  }
+
+  <label>
+    Telefoon
+    <input type="text" name="phone" [(ngModel)]="phone" />
+  </label>
+  @if (fieldErrors['phone']; as error) {
+    <p class="field-error" data-testid="field-error-phone">{{ error }}</p>
+  }
+
+  <label>
+    Voorkeurskanaal
+    <input type="text" name="preferredChannel" required [(ngModel)]="preferredChannel" />
+  </label>
+
+  <button type="submit">Opslaan</button>
+</form>