refactor: update services, alembic, scripts to use module imports

Update remaining application code to use canonical module locations:
- app/services/letzshop/order_service.py
- app/services/platform_health_service.py
- alembic/env.py (inventory and order models)
- scripts/investigate_order.py, verify_setup.py, seed_demo.py

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

app/services/letzshop/order_service.py

@@ -23,7 +23,7 @@ from models.database.letzshop import (
     VendorLetzshopCredentials,
 )
 from models.database.marketplace_import_job import MarketplaceImportJob
-from models.database.order import Order, OrderItem
+from app.modules.orders.models import Order, OrderItem
 from models.database.product import Product
 from models.database.vendor import Vendor
 

app/services/platform_health_service.py

@@ -17,8 +17,8 @@ from sqlalchemy import func, text
 from sqlalchemy.orm import Session
 
 from app.services.image_service import image_service
-from models.database.inventory import Inventory
-from models.database.order import Order
+from app.modules.inventory.models import Inventory
+from app.modules.orders.models import Order
 from models.database.product import Product
 from models.database.vendor import Vendor