Update all admin and vendor API routes to import schemas from
canonical module locations instead of legacy re-export files:
- messages: use app.modules.messaging.models/schemas
- customers: use app.modules.customers.schemas
- orders: use app.modules.orders.schemas
- inventory: use app.modules.inventory.schemas
- invoices: use app.modules.orders.schemas
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>