feat(persons): updatePerson rejects SKIP with INVALID_PERSON_TYPE

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

backend/src/main/java/org/raddatz/familienarchiv/service/PersonService.java

@@ -140,6 +140,9 @@ public class PersonService {
 
     @Transactional
     public Person updatePerson(UUID id, PersonUpdateDTO dto) {
+        if (dto.getPersonType() == PersonType.SKIP) {
+            throw DomainException.badRequest(ErrorCode.INVALID_PERSON_TYPE, "SKIP is not a valid person type for manual editing");
+        }
         validateYears(dto.getBirthYear(), dto.getDeathYear());
         Person person = personRepository.findById(id)
                 .orElseThrow(() -> DomainException.notFound(ErrorCode.PERSON_NOT_FOUND, "Person not found: " + id));