fix backup async

backend/src/main/java/com/storycove/service/AsyncBackupService.java

@@ -48,7 +48,10 @@ public class AsyncBackupService {
         BackupJob job = new BackupJob(libraryId, type);
         job = backupJobRepository.save(job);
 
-        // Start backup in background
+        // Force flush to ensure job is committed to DB before async execution
+        backupJobRepository.flush();
+
+        // Start backup in background (async method will run in separate thread after this transaction commits)
         executeBackupAsync(job.getId());
 
         return job;
@@ -58,7 +61,7 @@ public class AsyncBackupService {
      * Execute backup asynchronously
      */
     @Async
-    @Transactional
+    @Transactional(propagation = org.springframework.transaction.annotation.Propagation.REQUIRES_NEW)
     public void executeBackupAsync(UUID jobId) {
         Optional<BackupJob> jobOpt = backupJobRepository.findById(jobId);
         if (jobOpt.isEmpty()) {