style(registratie): WP-34 — BRP address as datablock, phone in grey fieldset

Restyle the contact-change form with house CIBG surfaces instead of hand-rolled
markup: the read-only BRP address now uses app-data-block/app-data-row (grey
datablock), and the phone field sits in a plain <fieldset> inside the existing
.form-horizontal form (inherits the CIBG grey box). No new CSS surfaces; row keys
reuse the address.* i18n ids. Logic/machine/specs unchanged.

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

docs/project/backlog/WP-34-adres-phone-brp-readonly.md

@@ -5,7 +5,7 @@ Phase: 7 — refinements
 
 ## Why
 
-The "Mijn gegevens" screen let the user *edit* their address (straat/postcode/woonplaats) and
+The "Mijn gegevens" screen let the user _edit_ their address (straat/postcode/woonplaats) and
 submit it as an adreswijziging. But the BRP (Basisregistratie Personen) is the authority for a
 person's address — you change it at the municipality, not in a register self-service portal.
 This WP corrects that: the address is shown **read-only** (rendered from the BRP data the