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>

backend/tests/BigRegister.Tests/EndpointTests.cs

@@ -101,20 +101,20 @@ public class EndpointTests(TestWebApplicationFactory factory) : IClassFixture<Te
   }
 
   [Fact]
-  public async Task Change_request_with_valid_address_succeeds()
+  public async Task Change_request_with_valid_phone_succeeds()
   {
     var res = await _client.PostAsJsonAsync("/api/v1/change-requests",
-        new { straat = "Lange Voorhout 9", postcode = "2514 EA", woonplaats = "Den Haag" });
+        new { telefoon = "0612345678" });
     res.EnsureSuccessStatusCode();
     var body = await res.Content.ReadFromJsonAsync<ReferentieResponse>();
     Assert.StartsWith("BIG-2026-", body!.Referentie);
   }
 
   [Fact]
-  public async Task Change_request_with_bad_postcode_is_rejected()
+  public async Task Change_request_with_bad_phone_is_rejected()
   {
     var res = await _client.PostAsJsonAsync("/api/v1/change-requests",
-        new { straat = "Straat 1", postcode = "nope", woonplaats = "Den Haag" });
+        new { telefoon = "nope" });
     Assert.Equal(HttpStatusCode.UnprocessableEntity, res.StatusCode);
   }
 

backend/tests/BigRegister.Tests/IdempotencyTests.cs

@@ -12,7 +12,7 @@ public class IdempotencyTests(TestWebApplicationFactory factory) : IClassFixture
   {
     var req = new HttpRequestMessage(HttpMethod.Post, "/api/v1/change-requests")
     {
-      Content = JsonContent.Create(new { straat = "Lange Voorhout 9", postcode = "2514 EA", woonplaats = "Den Haag" }),
+      Content = JsonContent.Create(new { telefoon = "0612345678" }),
     };
     req.Headers.Add("Idempotency-Key", key);
     return req;
@@ -51,7 +51,7 @@ public class IdempotencyTests(TestWebApplicationFactory factory) : IClassFixture
     var key = Guid.NewGuid().ToString();
     var badRequest = new HttpRequestMessage(HttpMethod.Post, "/api/v1/change-requests")
     {
-      Content = JsonContent.Create(new { straat = "Straat 1", postcode = "nope", woonplaats = "Den Haag" }),
+      Content = JsonContent.Create(new { telefoon = "nope" }),
     };
     badRequest.Headers.Add("Idempotency-Key", key);
 
@@ -60,7 +60,7 @@ public class IdempotencyTests(TestWebApplicationFactory factory) : IClassFixture
 
     var replayRequest = new HttpRequestMessage(HttpMethod.Post, "/api/v1/change-requests")
     {
-      Content = JsonContent.Create(new { straat = "Straat 1", postcode = "nope", woonplaats = "Den Haag" }),
+      Content = JsonContent.Create(new { telefoon = "nope" }),
     };
     replayRequest.Headers.Add("Idempotency-Key", key);
     var replay = await _client.SendAsync(replayRequest);

backend/tests/BigRegister.Tests/RuleTests.cs

@@ -172,9 +172,10 @@ public class SubmissionRuleTests
       Assert.Null(SubmissionRules.RejectZeroUren(40));
 
   [Theory]
-  [InlineData("Lange Voorhout 9", "2514 EA", null)]   // valid
-  [InlineData("", "2514 EA", "Vul straat en huisnummer in.")]
-  [InlineData("Straat 1", "nope", "Voer een geldige postcode in, bijv. 1234 AB.")]
-  public void Change_request_is_validated(string straat, string postcode, string? expected) =>
-      Assert.Equal(expected, SubmissionRules.RejectChangeRequest(straat, postcode));
+  [InlineData("0612345678", null)]              // valid mobile
+  [InlineData("070 123 45 67", null)]           // valid landline, formatting stripped
+  [InlineData("nope", "Voer een geldig telefoonnummer in, bijv. 0612345678.")]
+  [InlineData("12345", "Voer een geldig telefoonnummer in, bijv. 0612345678.")]
+  public void Phone_change_is_validated(string telefoon, string? expected) =>
+      Assert.Equal(expected, SubmissionRules.RejectPhoneChange(telefoon));
 }