style: apply black and isort formatting across entire codebase

- Standardize quote style (single to double quotes)
- Reorder and group imports alphabetically
- Fix line breaks and indentation for consistency
- Apply PEP 8 formatting standards

Also updated Makefile to exclude both venv and .venv from code quality checks.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

tests/unit/utils/test_csv_processor.py

@@ -18,7 +18,9 @@ class TestCSVProcessor:
     def test_download_csv_encoding_fallback(self, mock_get):
         """Test CSV download with encoding fallback"""
         # Create content with special characters that would fail UTF-8 if not properly encoded
-        special_content = "marketplace_product_id,title,price\nTEST001,Café MarketplaceProduct,10.99"
+        special_content = (
+            "marketplace_product_id,title,price\nTEST001,Café MarketplaceProduct,10.99"
+        )
 
         mock_response = Mock()
         mock_response.status_code = 200
@@ -40,9 +42,7 @@ class TestCSVProcessor:
         mock_response = Mock()
         mock_response.status_code = 200
         # Create bytes that will fail most encodings
-        mock_response.content = (
-            b"marketplace_product_id,title,price\nTEST001,\xff\xfe MarketplaceProduct,10.99"
-        )
+        mock_response.content = b"marketplace_product_id,title,price\nTEST001,\xff\xfe MarketplaceProduct,10.99"
         mock_response.raise_for_status.return_value = None
         mock_get.return_value = mock_response