refactor(relationship): use typed RelationType enum in CreateRelationshipRequest

Spring deserializes the enum directly; invalid values are caught by the
HttpMessageNotReadableException → 400 handler added in 99d00537, returning
a structured VALIDATION_ERROR. The manual parseType() helper is therefore
redundant and removed. Tests updated to construct requests with the enum.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

backend/src/main/java/org/raddatz/familienarchiv/relationship/RelationshipService.java

@@ -86,10 +86,9 @@ public class RelationshipService {
         Person person = personService.getById(personId);
         Person relatedPerson = personService.getById(dto.relatedPersonId());
 
-        RelationType type = parseType(dto.relationType());
         validateYears(dto.fromYear(), dto.toYear());
 
-        if (type == RelationType.PARENT_OF
+        if (dto.relationType() == RelationType.PARENT_OF
                 && relationshipRepository.existsByPersonIdAndRelatedPersonIdAndRelationType(
                         relatedPerson.getId(), personId, RelationType.PARENT_OF)) {
             throw DomainException.conflict(
@@ -100,7 +99,7 @@ public class RelationshipService {
         PersonRelationship rel = PersonRelationship.builder()
                 .person(person)
                 .relatedPerson(relatedPerson)
-                .relationType(type)
+                .relationType(dto.relationType())
                 .fromYear(dto.fromYear())
                 .toYear(dto.toYear())
                 .notes(blankToNull(dto.notes()))
@@ -113,7 +112,7 @@ public class RelationshipService {
         } catch (DataIntegrityViolationException e) {
             throw DomainException.conflict(
                     ErrorCode.DUPLICATE_RELATIONSHIP,
-                    "Relationship already exists for (" + personId + ", " + relatedPerson.getId() + ", " + type + ")");
+                    "Relationship already exists for (" + personId + ", " + relatedPerson.getId() + ", " + dto.relationType() + ")");
         }
     }
 
@@ -141,18 +140,6 @@ public class RelationshipService {
         return (s == null || s.isBlank()) ? null : s.trim();
     }
 
-    private static RelationType parseType(String typeName) {
-        if (typeName == null) {
-            throw DomainException.badRequest(ErrorCode.VALIDATION_ERROR, "relationType is required");
-        }
-        try {
-            return RelationType.valueOf(typeName);
-        } catch (IllegalArgumentException e) {
-            throw DomainException.badRequest(
-                    ErrorCode.VALIDATION_ERROR, "Invalid relationType: " + typeName);
-        }
-    }
-
     private static void validateYears(Integer fromYear, Integer toYear) {
         if (fromYear != null && toYear != null && toYear < fromYear) {
             throw DomainException.badRequest(

backend/src/main/java/org/raddatz/familienarchiv/relationship/dto/CreateRelationshipRequest.java

@@ -1,19 +1,14 @@
 package org.raddatz.familienarchiv.relationship.dto;
 
-import jakarta.validation.constraints.NotBlank;
 import jakarta.validation.constraints.NotNull;
 import jakarta.validation.constraints.Size;
+import org.raddatz.familienarchiv.relationship.RelationType;
 
 import java.util.UUID;
 
-/**
- * POST body for {@code /api/persons/{id}/relationships}. {@code relationType}
- * is a string here; the controller validates it against the {@code RelationType}
- * enum at the boundary.
- */
 public record CreateRelationshipRequest(
         @NotNull UUID relatedPersonId,
-        @NotBlank String relationType,
+        @NotNull RelationType relationType,
         Integer fromYear,
         Integer toYear,
         @Size(max = 2000) String notes