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/unit/services/test_customer_address_service.py

@@ -8,7 +8,7 @@ import pytest
 from app.exceptions import AddressLimitExceededException, AddressNotFoundException
 from app.services.customer_address_service import CustomerAddressService
 from app.modules.customers.models.customer import CustomerAddress
-from models.schema.customer import CustomerAddressCreate, CustomerAddressUpdate
+from app.modules.customers.schemas import CustomerAddressCreate, CustomerAddressUpdate
 
 
 @pytest.fixture