fix: ruff lint + format fixes in tests, ESLint fixes in frontend

backend/app/services/datev_service.py

@@ -60,9 +60,7 @@ async def create_export(
     csv_content = generate_datev_csv(sales)
 
     # Calculate total amount
-    total_amount = sum(
-        (s.sale_price or Decimal("0")) for s in sales
-    )
+    total_amount = sum((s.sale_price or Decimal("0")) for s in sales)
 
     # Save CSV file
     os.makedirs(output_dir, exist_ok=True)
@@ -111,7 +109,9 @@ async def list_exports(
     return exports, total
 
 
-async def get_export_csv(db: AsyncSession, export_id: uuid.UUID) -> tuple[str, bytes] | None:
+async def get_export_csv(
+    db: AsyncSession, export_id: uuid.UUID
+) -> tuple[str, bytes] | None:
     """Get the CSV content for a DATEV export.
 
     Args: