feat(persons): createPerson(DTO) 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

@@ -128,6 +128,17 @@ class PersonServiceTest {
         assertThat(result.getPersonType()).isEqualTo(PersonType.INSTITUTION);
     }
 
+    @Test
+    void createPerson_dto_throwsInvalidPersonType_whenSkip() {
+        PersonUpdateDTO dto = new PersonUpdateDTO();
+        dto.setFirstName("Anna"); dto.setLastName("Test"); dto.setPersonType(PersonType.SKIP);
+
+        assertThatThrownBy(() -> personService.createPerson(dto))
+                .isInstanceOf(DomainException.class)
+                .extracting(e -> ((DomainException) e).getStatus().value())
+                .isEqualTo(400);
+    }
+
     @Test
     void createPerson_dto_persistsTitle() {
         when(personRepository.save(any())).thenAnswer(inv -> inv.getArgument(0));