fix(document): break DocumentService ↔ ThumbnailAsyncRunner ↔ ThumbnailService cycle

Spring Framework 7 prohibits constructor injection cycles even with @Lazy.
Replace DocumentService dependencies in ThumbnailAsyncRunner and ThumbnailService
with direct DocumentRepository calls — both are intra-domain reads/saves.
Update ThumbnailServiceTest to mock DocumentRepository accordingly.

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

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

@@ -29,7 +29,6 @@ import org.raddatz.familienarchiv.ocr.TrainingLabel;
 import org.raddatz.familienarchiv.person.Person;
 import org.raddatz.familienarchiv.tag.Tag;
 import org.raddatz.familienarchiv.document.DocumentRepository;
-import org.springframework.context.annotation.Lazy;
 import org.springframework.data.domain.Page;
 import org.springframework.data.domain.PageRequest;
 import org.springframework.data.domain.Pageable;
@@ -77,10 +76,6 @@ public class DocumentService {
     private final AuditService auditService;
     private final TranscriptionBlockQueryService transcriptionBlockQueryService;
     private final AuditLogQueryService auditLogQueryService;
-    // @Lazy breaks the DocumentService ↔ ThumbnailAsyncRunner cycle: the runner
-    // now reaches Document data through DocumentService (per the layering rule),
-    // and Spring needs a proxy here to defer the back-edge until both beans exist.
-    @Lazy
     private final ThumbnailAsyncRunner thumbnailAsyncRunner;
 
     public record StoreResult(Document document, boolean isNew) {}

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

@@ -28,7 +28,7 @@ import java.util.concurrent.TimeoutException;
 @Slf4j
 public class ThumbnailAsyncRunner {
 
-    private final DocumentService documentService;
+    private final DocumentRepository documentRepository;
     private final ThumbnailService thumbnailService;
 
     /** Per-document timeout for the whole generate() call — defense against corrupt PDFs. */
@@ -59,7 +59,7 @@ public class ThumbnailAsyncRunner {
      */
     @Async("thumbnailExecutor")
     public void generateAsync(UUID documentId) {
-        Optional<Document> docOpt = documentService.findById(documentId);
+        Optional<Document> docOpt = documentRepository.findById(documentId);
         if (docOpt.isEmpty()) {
             log.warn("Thumbnail generation skipped: document not found id={}", documentId);
             return;

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

@@ -62,16 +62,16 @@ public class ThumbnailService {
 
     private final FileService fileService;
     private final S3Client s3Client;
-    private final DocumentService documentService;
+    private final DocumentRepository documentRepository;
 
     @Value("${app.s3.bucket}")
     private String bucketName;
 
     public ThumbnailService(FileService fileService, S3Client s3Client,
-                            DocumentService documentService) {
+                            DocumentRepository documentRepository) {
         this.fileService = fileService;
         this.s3Client = s3Client;
-        this.documentService = documentService;
+        this.documentRepository = documentRepository;
     }
 
     public Outcome generate(Document doc) {
@@ -167,7 +167,7 @@ public class ThumbnailService {
             doc.setThumbnailGeneratedAt(LocalDateTime.now());
             doc.setThumbnailAspect(result.aspect());
             doc.setPageCount(result.pageCount());
-            documentService.updateThumbnailMetadata(doc);
+            documentRepository.save(doc);
             return Outcome.SUCCESS;
         } catch (Exception e) {
             // Thumbnail is already in S3 but the entity update failed. Because the S3