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/vendor/test_invoices.py

@@ -10,8 +10,8 @@ from decimal import Decimal
 import pytest
 
 from app.modules.customers.models.customer import Customer
-from models.database.invoice import Invoice, InvoiceStatus, VendorInvoiceSettings
-from models.database.order import Order
+from app.modules.orders.models import Invoice, InvoiceStatus, VendorInvoiceSettings
+from app.modules.orders.models import Order
 
 
 @pytest.mark.integration

tests/integration/api/v1/vendor/test_letzshop.py

@@ -240,7 +240,7 @@ class TestVendorLetzshopOrdersAPI:
         """Test listing orders with status filter."""
         from datetime import datetime, timezone
 
-        from models.database.order import Order
+        from app.modules.orders.models import Order
 
         # Create test orders using unified Order model with all required fields
         order1 = Order(
@@ -315,7 +315,7 @@ class TestVendorLetzshopOrdersAPI:
         """Test getting order detail."""
         from datetime import datetime, timezone
 
-        from models.database.order import Order
+        from app.modules.orders.models import Order
 
         order = Order(
             vendor_id=test_vendor_with_vendor_user.id,
@@ -457,7 +457,7 @@ class TestVendorLetzshopFulfillmentAPI:
         """Test confirming an order."""
         from datetime import datetime, timezone
 
-        from models.database.order import Order, OrderItem
+        from app.modules.orders.models import Order, OrderItem
 
         # Create test order using unified Order model with all required fields
         order = Order(
@@ -546,7 +546,7 @@ class TestVendorLetzshopFulfillmentAPI:
         """Test setting tracking information."""
         from datetime import datetime, timezone
 
-        from models.database.order import Order
+        from app.modules.orders.models import Order
 
         order = Order(
             vendor_id=test_vendor_with_vendor_user.id,

tests/integration/api/v1/vendor/test_messages.py

@@ -7,7 +7,7 @@ Tests the /api/v1/vendor/messages/* endpoints.
 
 import pytest
 
-from models.database.message import ConversationType, ParticipantType
+from app.modules.messaging.models import ConversationType, ParticipantType
 
 
 @pytest.mark.integration

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

@@ -5,7 +5,7 @@ from datetime import UTC, datetime
 
 import pytest
 
-from models.database.order import Order, OrderItem
+from app.modules.orders.models import Order, OrderItem
 
 
 @pytest.fixture