refine backup script

scripts/backup_db.sh

@@ -74,7 +74,7 @@ done
 
 if [ -n "${BACKUP_REMOTE:-}" ]; then
   remote_target=${BACKUP_REMOTE%/}/$(basename "$FINAL_BACKUP")
-  rclone copyto "$FINAL_BACKUP" "$remote_target"
+  rclone sync "$FINAL_BACKUP" "$remote_target"
   echo "Backup uploaded to remote: $remote_target"
 else
   echo "BACKUP_REMOTE is empty; skipping remote upload"