feat(registratie): WP-34 — phone field + BRP address read-only

Reshape the adreswijziging form into a contact-change form: the BRP address is
authoritative and shown read-only (you change it at the gemeente), and the phone
number becomes the editable/submittable field. New Telefoonnummer value object
(parse-don't-validate); backend RejectPhoneChange re-validates as authority.
POST /change-requests now carries { telefoon } (typed client regenerated).

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

src/app/shared/infrastructure/api-client.ts

@@ -1721,9 +1721,7 @@ export interface CaseContextDto {
 }
 
 export interface ChangeRequestRequest {
-    straat?: string | undefined;
-    postcode?: string | undefined;
-    woonplaats?: string | undefined;
+    telefoon?: string | undefined;
 }
 
 export interface CreateApplicationRequest {