refactor(ocr): extract exportSenderData helper in triggerSenderTraining

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

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

@@ -126,10 +126,7 @@ public class SenderModelService {
         log.info("Started sender training run {} for person {}", runId, personId);
 
         try {
-            ByteArrayOutputStream baos = new ByteArrayOutputStream();
-            trainingDataExportService.exportForSender(personId).writeTo(baos);
-            byte[] zipBytes = baos.toByteArray();
-
+            byte[] zipBytes = exportSenderData(personId);
             log.info("[trainingRun={}] Sending {} bytes to OCR service for sender training", runId, zipBytes.length);
             OcrClient.TrainingResult result = ocrClient.trainSenderModel(zipBytes, outputModelPath);
 
@@ -166,6 +163,12 @@ public class SenderModelService {
         }
     }
 
+    private byte[] exportSenderData(UUID personId) throws java.io.IOException {
+        ByteArrayOutputStream baos = new ByteArrayOutputStream();
+        trainingDataExportService.exportForSender(personId).writeTo(baos);
+        return baos.toByteArray();
+    }
+
     /**
      * Promotes the oldest QUEUED sender run to RUNNING and triggers its training.
      * Called in the finally block of triggerSenderTraining, creating a sequential chain: