feat(persons): updatePerson rejects SKIP with INVALID_PERSON_TYPE

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/src/test/java/org/raddatz/familienarchiv/service/PersonServiceTest.java

@@ -184,6 +184,19 @@ class PersonServiceTest {
 
     // ─── updatePerson (personType) ───────────────────────────────────────────
 
+    @Test
+    void updatePerson_throwsInvalidPersonType_whenSkip() {
+        UUID id = UUID.randomUUID();
+
+        PersonUpdateDTO dto = new PersonUpdateDTO();
+        dto.setFirstName("Anna"); dto.setLastName("Alt"); dto.setPersonType(PersonType.SKIP);
+
+        assertThatThrownBy(() -> personService.updatePerson(id, dto))
+                .isInstanceOf(DomainException.class)
+                .extracting(e -> ((DomainException) e).getStatus().value())
+                .isEqualTo(400);
+    }
+
     @Test
     void updatePerson_persistsPersonType() {
         UUID id = UUID.randomUUID();