refactor: update test imports to use module locations

Update all test files to import from canonical module locations:
- Integration tests: orders, inventory, messages, invoices
- Unit tests: services and models
- Fixtures: customer, vendor, message fixtures

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

tests/integration/api/v1/storefront/test_orders.py

@@ -13,8 +13,8 @@ import pytest
 from jose import jwt
 
 from app.modules.customers.models.customer import Customer
-from models.database.invoice import Invoice, InvoiceStatus, VendorInvoiceSettings
-from models.database.order import Order, OrderItem
+from app.modules.orders.models import Invoice, InvoiceStatus, VendorInvoiceSettings
+from app.modules.orders.models import Order, OrderItem
 
 
 @pytest.fixture