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>

alembic/env.py

@@ -125,7 +125,7 @@ except ImportError as e:
 # INVENTORY MODEL
 # ----------------------------------------------------------------------------
 try:
-    from models.database.inventory import Inventory
+    from app.modules.inventory.models import Inventory
 
     print("  ✓ Inventory model imported")
 except ImportError as e:
@@ -168,7 +168,7 @@ except ImportError as e:
 # ORDER MODELS
 # ----------------------------------------------------------------------------
 try:
-    from models.database.order import Order, OrderItem
+    from app.modules.orders.models import Order, OrderItem
 
     print("  ✓ Order models imported (2 models)")
     print("    - Order")