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>

scripts/seed_demo.py

@@ -60,7 +60,7 @@ from models.database.marketplace_product import MarketplaceProduct
 from models.database.marketplace_product_translation import (
     MarketplaceProductTranslation,
 )
-from models.database.order import Order, OrderItem
+from app.modules.orders.models import Order, OrderItem
 from models.database.product import Product
 from models.database.user import User
 from models.database.vendor import Role, Vendor, VendorUser