refactor: delete legacy re-export files for migrated modules

All imports have been updated to use canonical module locations.
Delete 15 legacy re-export files that are no longer needed:

Database models (7 files):
- models/database/order.py
- models/database/inventory.py
- models/database/inventory_transaction.py
- models/database/message.py
- models/database/invoice.py
- models/database/order_item_exception.py
- models/database/password_reset_token.py

Schema models (8 files):
- models/schema/customer.py
- models/schema/order.py
- models/schema/order_item_exception.py
- models/schema/inventory.py
- models/schema/message.py
- models/schema/invoice.py
- models/schema/notification.py
- models/schema/stats.py

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

models/schema/product.py

@@ -3,7 +3,7 @@ from datetime import datetime
 
 from pydantic import BaseModel, ConfigDict, Field
 
-from models.schema.inventory import InventoryLocationResponse
+from app.modules.inventory.schemas import InventoryLocationResponse
 from models.schema.marketplace_product import MarketplaceProductResponse