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/models/test_database_models.py

@@ -1,16 +1,17 @@
 # tests/unit/models/test_database_models.py
-import pytest
 from datetime import datetime, timezone
+
+import pytest
 from sqlalchemy.exc import IntegrityError
 
-from models.database.marketplace_product import MarketplaceProduct
-from models.database.vendor import Vendor, VendorUser, Role
-from models.database.inventory import Inventory
-from models.database.user import User
-from models.database.marketplace_import_job import MarketplaceImportJob
-from models.database.product import Product
 from models.database.customer import Customer, CustomerAddress
+from models.database.inventory import Inventory
+from models.database.marketplace_import_job import MarketplaceImportJob
+from models.database.marketplace_product import MarketplaceProduct
 from models.database.order import Order, OrderItem
+from models.database.product import Product
+from models.database.user import User
+from models.database.vendor import Role, Vendor, VendorUser
 
 
 @pytest.mark.unit
@@ -277,7 +278,7 @@ class TestMarketplaceProductModel:
             vendor_id=test_vendor.id,
             marketplace_product_id="UNIQUE_001",
             title="Product 1",
-            marketplace="Letzshop"
+            marketplace="Letzshop",
         )
         db.add(product1)
         db.commit()
@@ -288,7 +289,7 @@ class TestMarketplaceProductModel:
                 vendor_id=test_vendor.id,
                 marketplace_product_id="UNIQUE_001",
                 title="Product 2",
-                marketplace="Letzshop"
+                marketplace="Letzshop",
             )
             db.add(product2)
             db.commit()
@@ -515,7 +516,9 @@ class TestCustomerModel:
 class TestOrderModel:
     """Test Order model"""
 
-    def test_order_creation(self, db, test_vendor, test_customer, test_customer_address):
+    def test_order_creation(
+        self, db, test_vendor, test_customer, test_customer_address
+    ):
         """Test Order model with customer relationship"""
         order = Order(
             vendor_id=test_vendor.id,
@@ -563,7 +566,9 @@ class TestOrderModel:
         assert float(order_item.unit_price) == 49.99
         assert float(order_item.total_price) == 99.98
 
-    def test_order_number_uniqueness(self, db, test_vendor, test_customer, test_customer_address):
+    def test_order_number_uniqueness(
+        self, db, test_vendor, test_customer, test_customer_address
+    ):
         """Test order_number unique constraint"""
         order1 = Order(
             vendor_id=test_vendor.id,