I need an experienced Node.js and Express developer to create a robust backend for a multi-tenant SaaS travel itinerary builder. The backend should provide user registration and authentication, allow for custom itinerary creation and saving, and support multi-tenant functionality with separate data management for each tenant. We will use postgresql Tenants should have the ability to customize travel templates and set different access roles for their users. Additionally, the backend must integrate third-party APIs for services like flight or hotel bookings. I already have HTML demos to guide the functionality, and the frontend will be developed once the backend is completed. I'm ready to get started immediately. This will be an ongoing project.