feat(relationship): add generation to PersonNodeDTO + update all sites (#689)

PersonNodeDTO is a positional record. The optional Integer generation
field is inserted between deathYear and familyMember so all four
construction sites stay readable without a builder.

- RelationshipService.getFamilyNetwork → populates with
  person.getGeneration() (the Stammbaum's strict-rank source on the
  frontend).
- RelationshipInferenceService.findAllFor → populates the same way;
  inference UI does not consume it but the field travels along for
  consistency.
- RelationshipControllerTest fixtures pass null.

Refs #689

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

backend/src/main/java/org/raddatz/familienarchiv/person/relationship/RelationshipInferenceService.java

@@ -96,7 +96,8 @@ public class RelationshipInferenceService {
             if (p == null) continue;
             List<RelationToken> path = shortestPaths.get(id);
             PersonNodeDTO node = new PersonNodeDTO(
-                    p.getId(), p.getDisplayName(), p.getBirthYear(), p.getDeathYear(), p.isFamilyMember());
+                    p.getId(), p.getDisplayName(), p.getBirthYear(), p.getDeathYear(),
+                    p.getGeneration(), p.isFamilyMember());
             out.add(new InferredRelationshipWithPersonDTO(node, labelFor(path), path.size()));
         }
         out.sort(Comparator.comparingInt(InferredRelationshipWithPersonDTO::hops)

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

@@ -66,7 +66,8 @@ public class RelationshipService {
         for (Person p : familyMembers) {
             familyIds.add(p.getId());
             nodes.add(new PersonNodeDTO(
-                    p.getId(), p.getDisplayName(), p.getBirthYear(), p.getDeathYear(), true));
+                    p.getId(), p.getDisplayName(), p.getBirthYear(), p.getDeathYear(),
+                    p.getGeneration(), true));
         }
 
         List<PersonRelationship> familyEdges = relationshipRepository.findAllByRelationTypeIn(

backend/src/main/java/org/raddatz/familienarchiv/person/relationship/dto/PersonNodeDTO.java

@@ -10,5 +10,6 @@ public record PersonNodeDTO(
         @Schema(requiredMode = Schema.RequiredMode.REQUIRED) String displayName,
         Integer birthYear,
         Integer deathYear,
+        Integer generation,
         @Schema(requiredMode = Schema.RequiredMode.REQUIRED) boolean familyMember
 ) {}