feat(behandelportal): WP-63 aanvraag status lifecycle enum

Model the full ADR-0002 lifecycle (Ingediend/InBehandeling/
MeerInfoGevraagd/Goedgekeurd/Afgewezen) as a backend enum backing the
existing AanvraagStatusDto.Tag string, and widen the FE union/parse
boundary/switches to match. Ingediend/MeerInfoGevraagd aren't reachable
yet (no behandelaar transition exists) — that's WP-65. Zero DTO shape
change, so gen:api has no drift.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

backend/tests/BigRegister.Tests/ApplicationTests.cs

@@ -205,4 +205,15 @@ public class ApplicationTests(TestWebApplicationFactory factory) : IClassFixture
     Assert.Equal("InBehandeling", status.Tag);
     Assert.True(status.Manual);
   }
+
+  // WP-63: the published lifecycle (ADR-0002) must name exactly these five tags, in this
+  // order — ToStatusDto's string literals must keep matching Enum.ToString(), and Ingediend/
+  // MeerInfoGevraagd (unreachable until WP-65 adds the behandelaar transition) stay defined.
+  [Fact]
+  public void AanvraagStatusTag_covers_the_published_lifecycle()
+  {
+    Assert.Equal(
+        new[] { "Ingediend", "InBehandeling", "MeerInfoGevraagd", "Goedgekeurd", "Afgewezen" },
+        Enum.GetNames<AanvraagStatusTag>());
+  }
 }