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>

docs/project/backlog/README.md

@@ -78,7 +78,7 @@ for its existing violations, so every WP ends green.
 | [WP-31](WP-31-shared-store-helpers.md)     | Shared store helpers (ActionState/SaveState, history, debounced-save, RemoteData) | 7 · refinements             | done   |
 | [WP-32](WP-32-stamdata-undo.md)            | Undo/redo in the stamdata editor                                                  | 7 · refinements             | done   |
 | [WP-33](WP-33-dev-switchers.md)            | In-app dev switchers (scenario + role)                                            | 7 · refinements             | done   |
-| [WP-34](WP-34-adres-phone-brp-readonly.md) | Adres: phone field + BRP address read-only                                        | 7 · refinements             | todo   |
+| [WP-34](WP-34-adres-phone-brp-readonly.md) | Adres: phone field + BRP address read-only                                        | 7 · refinements             | done   |
 | [WP-35](WP-35-one-concept-per-type.md)     | One Concept per case type (server-enforced)                                       | 7 · refinements             | todo   |
 | [WP-36](WP-36-admin-cases.md)              | Admin cases page + admin delete                                                   | 7 · refinements             | todo   |