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/fixtures/vendor_fixtures.py

@@ -1,10 +1,11 @@
 # tests/fixtures/vendor_fixtures.py
 import uuid
+
 import pytest
 
-from models.database.vendor import Vendor
-from models.database.product import Product
 from models.database.inventory import Inventory
+from models.database.product import Product
+from models.database.vendor import Vendor
 
 
 @pytest.fixture
@@ -185,6 +186,7 @@ def multiple_inventory_entries(db, multiple_products, test_vendor):
 
 def create_unique_vendor_factory():
     """Factory function to create unique vendors in tests"""
+
     def _create_vendor(db, owner_user_id, **kwargs):
         unique_id = str(uuid.uuid4())[:8]
         defaults = {