style: sort two import blocks the download cleanup left out of order

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/test_download_service.py

@@ -1057,8 +1057,8 @@ async def test_partial_error_type_maps_to_ok_status(
     """A non-zero gallery-dl exit accompanied by PARTIAL error_type
     (real files were downloaded before the run was cut short) is treated
     as status=ok by the orchestrator — next tick continues."""
-    from backend.app.services.download_service import DownloadService
     from backend.app.services.download_result import ErrorType
+    from backend.app.services.download_service import DownloadService
     from backend.app.services.importer import Importer
 
     _artist, source = seed_artist_and_source