feat(model): add title field to PersonUpdateDTO with @Size validation

Add title to PersonUpdateDTO with @Size(max=50) constraint.
PersonService.createPerson and updatePerson now handle the title
field with blank-to-null normalization.

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

backend/src/main/java/org/raddatz/familienarchiv/dto/PersonUpdateDTO.java

@@ -5,6 +5,8 @@ import lombok.Data;
 
 @Data
 public class PersonUpdateDTO {
+    @Size(max = 50)
+    private String title;
     @Size(max = 100)
     private String firstName;
     @Size(max = 100)

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

@@ -111,6 +111,7 @@ public class PersonService {
     public Person createPerson(PersonUpdateDTO dto) {
         validateYears(dto.getBirthYear(), dto.getDeathYear());
         Person person = Person.builder()
+                .title(dto.getTitle() == null || dto.getTitle().isBlank() ? null : dto.getTitle().trim())
                 .firstName(dto.getFirstName())
                 .lastName(dto.getLastName())
                 .alias(dto.getAlias() == null || dto.getAlias().isBlank() ? null : dto.getAlias().trim())
@@ -138,6 +139,7 @@ public class PersonService {
         validateYears(dto.getBirthYear(), dto.getDeathYear());
         Person person = personRepository.findById(id)
                 .orElseThrow(() -> DomainException.notFound(ErrorCode.PERSON_NOT_FOUND, "Person not found: " + id));
+        person.setTitle(dto.getTitle() == null || dto.getTitle().isBlank() ? null : dto.getTitle().trim());
         person.setFirstName(dto.getFirstName());
         person.setLastName(dto.getLastName());
         person.setAlias(dto.getAlias() == null || dto.getAlias().isBlank() ? null : dto.getAlias().trim());