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/models/database/test_inventory.py

@@ -4,7 +4,7 @@
 import pytest
 from sqlalchemy.exc import IntegrityError
 
-from models.database.inventory import Inventory
+from app.modules.inventory.models import Inventory
 
 
 @pytest.mark.unit

tests/unit/models/database/test_order.py

@@ -6,7 +6,7 @@ from datetime import datetime, timezone
 import pytest
 from sqlalchemy.exc import IntegrityError
 
-from models.database.order import Order, OrderItem
+from app.modules.orders.models import Order, OrderItem
 
 
 def create_order_with_snapshots(

tests/unit/models/database/test_order_item_exception.py

@@ -4,7 +4,7 @@
 import pytest
 from sqlalchemy.exc import IntegrityError
 
-from models.database.order_item_exception import OrderItemException
+from app.modules.orders.models import OrderItemException
 
 
 @pytest.mark.unit
@@ -65,7 +65,7 @@ class TestOrderItemExceptionModel:
         exception_types = ["product_not_found", "gtin_mismatch", "duplicate_gtin"]
 
         # Create new order items for each test to avoid unique constraint
-        from models.database.order import OrderItem
+        from app.modules.orders.models import OrderItem
 
         for i, exc_type in enumerate(exception_types):
             order_item = OrderItem(

tests/unit/models/database/test_product.py

@@ -306,7 +306,7 @@ class TestProductInventoryProperties:
 
     def test_physical_product_with_inventory(self, db, test_vendor):
         """Test physical product calculates inventory from entries."""
-        from models.database.inventory import Inventory
+        from app.modules.inventory.models import Inventory
 
         product = Product(
             vendor_id=test_vendor.id,
@@ -364,7 +364,7 @@ class TestProductInventoryProperties:
 
     def test_digital_product_ignores_inventory_entries(self, db, test_vendor):
         """Test digital product returns unlimited even with inventory entries."""
-        from models.database.inventory import Inventory
+        from app.modules.inventory.models import Inventory
 
         product = Product(
             vendor_id=test_vendor.id,