fix(fc3c): ruff — split SyncSession import, StrEnum, ASYNC240 noqa, blank-line

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

backend/app/services/gallery_dl.py

@@ -19,7 +19,7 @@ import tempfile
 import time
 from dataclasses import dataclass, field
 from datetime import UTC, datetime
-from enum import Enum
+from enum import StrEnum
 from pathlib import Path
 
 from .file_validator import is_validatable, validate_file
@@ -27,7 +27,7 @@ from .file_validator import is_validatable, validate_file
 log = logging.getLogger(__name__)
 
 
-class ErrorType(str, Enum):
+class ErrorType(StrEnum):
     AUTH_ERROR = "auth_error"
     RATE_LIMITED = "rate_limited"
     NOT_FOUND = "not_found"
@@ -655,6 +655,6 @@ class GalleryDLService:
             )
         finally:
             try:
-                Path(temp_config_path).unlink()
+                Path(temp_config_path).unlink()  # noqa: ASYNC240
             except Exception:
                 pass