refactor(thumbnail): route document access through DocumentService

The Thumbnail trio (ThumbnailService, ThumbnailBackfillService,
ThumbnailAsyncRunner) all injected DocumentRepository directly. They now go
through three new DocumentService delegations:

- findById(UUID): Optional<Document> — no-throw variant for the runner's
  log-and-skip behaviour on missing documents.
- findForThumbnailBackfill() — wraps the existing
  findByFilePathIsNotNullAndThumbnailKeyIsNull query.
- updateThumbnailMetadata(Document) — wraps save() for the post-thumbnail
  entity update.

DocumentService also gains @Lazy on its existing ThumbnailAsyncRunner field
to break the new DocumentService ↔ ThumbnailAsyncRunner cycle. lombok.config
adds @Lazy to copyableAnnotations so the field annotation reaches the
generated constructor parameter.

Refs #417 (C6.2 violations #2, #3, #4).

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

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

@@ -25,6 +25,7 @@ import org.raddatz.familienarchiv.model.TrainingLabel;
 import org.raddatz.familienarchiv.model.Person;
 import org.raddatz.familienarchiv.model.Tag;
 import org.raddatz.familienarchiv.repository.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;
@@ -69,6 +70,10 @@ 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) {}
@@ -77,6 +82,18 @@ public class DocumentService {
         return documentRepository.count();
     }
 
+    public Optional<Document> findById(UUID id) {
+        return documentRepository.findById(id);
+    }
+
+    public List<Document> findForThumbnailBackfill() {
+        return documentRepository.findByFilePathIsNotNullAndThumbnailKeyIsNull();
+    }
+
+    public Document updateThumbnailMetadata(Document doc) {
+        return documentRepository.save(doc);
+    }
+
     public Map<UUID, String> findTitlesByIds(Collection<UUID> ids) {
         if (ids.isEmpty()) return Map.of();
         Map<UUID, String> titles = new HashMap<>();

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

@@ -3,7 +3,6 @@ package org.raddatz.familienarchiv.service;
 import lombok.RequiredArgsConstructor;
 import lombok.extern.slf4j.Slf4j;
 import org.raddatz.familienarchiv.model.Document;
-import org.raddatz.familienarchiv.repository.DocumentRepository;
 import org.springframework.scheduling.annotation.Async;
 import org.springframework.stereotype.Service;
 import org.springframework.transaction.support.TransactionSynchronization;
@@ -29,7 +28,7 @@ import java.util.concurrent.TimeoutException;
 @Slf4j
 public class ThumbnailAsyncRunner {
 
-    private final DocumentRepository documentRepository;
+    private final DocumentService documentService;
     private final ThumbnailService thumbnailService;
 
     /** Per-document timeout for the whole generate() call — defense against corrupt PDFs. */
@@ -60,7 +59,7 @@ public class ThumbnailAsyncRunner {
      */
     @Async("thumbnailExecutor")
     public void generateAsync(UUID documentId) {
-        Optional<Document> docOpt = documentRepository.findById(documentId);
+        Optional<Document> docOpt = documentService.findById(documentId);
         if (docOpt.isEmpty()) {
             log.warn("Thumbnail generation skipped: document not found id={}", documentId);
             return;

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

@@ -5,7 +5,6 @@ import lombok.extern.slf4j.Slf4j;
 import org.raddatz.familienarchiv.exception.DomainException;
 import org.raddatz.familienarchiv.exception.ErrorCode;
 import org.raddatz.familienarchiv.model.Document;
-import org.raddatz.familienarchiv.repository.DocumentRepository;
 import org.springframework.scheduling.annotation.Async;
 import org.springframework.stereotype.Service;
 
@@ -37,7 +36,7 @@ public class ThumbnailBackfillService {
             LocalDateTime startedAt
     ) {}
 
-    private final DocumentRepository documentRepository;
+    private final DocumentService documentService;
     private final ThumbnailService thumbnailService;
 
     private volatile BackfillStatus currentStatus = new BackfillStatus(
@@ -57,7 +56,7 @@ public class ThumbnailBackfillService {
         LocalDateTime startedAt = LocalDateTime.now();
         List<Document> docs;
         try {
-            docs = documentRepository.findByFilePathIsNotNullAndThumbnailKeyIsNull();
+            docs = documentService.findForThumbnailBackfill();
         } catch (Exception e) {
             currentStatus = new BackfillStatus(State.FAILED,
                     "Backfill fehlgeschlagen: " + e.getMessage(),

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

@@ -8,7 +8,6 @@ import org.apache.pdfbox.rendering.ImageType;
 import org.apache.pdfbox.rendering.PDFRenderer;
 import org.raddatz.familienarchiv.model.Document;
 import org.raddatz.familienarchiv.model.ThumbnailAspect;
-import org.raddatz.familienarchiv.repository.DocumentRepository;
 import org.springframework.beans.factory.annotation.Value;
 import org.springframework.stereotype.Service;
 import software.amazon.awssdk.core.sync.RequestBody;
@@ -62,16 +61,16 @@ public class ThumbnailService {
 
     private final FileService fileService;
     private final S3Client s3Client;
-    private final DocumentRepository documentRepository;
+    private final DocumentService documentService;
 
     @Value("${app.s3.bucket}")
     private String bucketName;
 
     public ThumbnailService(FileService fileService, S3Client s3Client,
-                            DocumentRepository documentRepository) {
+                            DocumentService documentService) {
         this.fileService = fileService;
         this.s3Client = s3Client;
-        this.documentRepository = documentRepository;
+        this.documentService = documentService;
     }
 
     public Outcome generate(Document doc) {
@@ -167,7 +166,7 @@ public class ThumbnailService {
             doc.setThumbnailGeneratedAt(LocalDateTime.now());
             doc.setThumbnailAspect(result.aspect());
             doc.setPageCount(result.pageCount());
-            documentRepository.save(doc);
+            documentService.updateThumbnailMetadata(doc);
             return Outcome.SUCCESS;
         } catch (Exception e) {
             // Thumbnail is already in S3 but the entity update failed. Because the S3