chore(document): address non-blocking review feedback on lazy-fetch PR

- Add @BatchSize(50) fallback comments on findBySenderId / findByReceiversId
- Replace silent size() discard in getRecentActivity test with assertThat isNotEmpty()
- Add ADR-022 reference comment above @JsonIgnoreProperties on Person and Tag
- Document within-open-transaction limitation in DocumentLazyLoadingTest Javadoc

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

backend/src/main/java/org/raddatz/familienarchiv/document/DocumentRepository.java

@@ -50,9 +50,11 @@ public interface DocumentRepository extends JpaRepository<Document, UUID>, JpaSp
     // Prüft effizient, ob ein Dateiname schon existiert (gibt true/false zurück)
     boolean existsByOriginalFilename(String originalFilename);
 
+    // lazy – @BatchSize(50) fallback active; see ADR-022
     @EntityGraph("Document.full")
     List<Document> findBySenderId(UUID senderId);
 
+    // lazy – @BatchSize(50) fallback active; see ADR-022
     @EntityGraph("Document.full")
     List<Document> findByReceiversId(UUID receiverId);
 

backend/src/main/java/org/raddatz/familienarchiv/person/Person.java

@@ -11,6 +11,7 @@ import java.util.ArrayList;
 import java.util.List;
 import java.util.UUID;
 
+// prevents infinite recursion in JSON serialization; see ADR-022 for lazy-fetch context
 @JsonIgnoreProperties({"hibernateLazyInitializer", "handler"})
 @Entity
 @Table(name = "persons")

backend/src/main/java/org/raddatz/familienarchiv/tag/Tag.java

@@ -7,6 +7,7 @@ import io.swagger.v3.oas.annotations.media.Schema;
 import jakarta.persistence.*;
 import lombok.*;
 
+// prevents infinite recursion in JSON serialization; see ADR-022 for lazy-fetch context
 @JsonIgnoreProperties({"hibernateLazyInitializer", "handler"})
 @Entity
 @Data