Senior backend/fullstack developer

I am looking for a senior backend/fullstack developer to build a production-level SaaS system with heavy AI integration and complex automation workflows.

The system includes:
- AI-driven conversational flow (OpenAI)
- Integration with external APIs (including messaging platforms)
- File upload and document processing (including OCR/AI analysis)
- Complex business logic and decision engine (state machine-based workflows)
- Payment integration (Stripe)
- User management and authentication
- Dashboard for internal operations
- Background job processing (queues)

Key requirements:
- Strong experience with Node.js (mandatory)
- Experience building scalable backend systems
- Deep understanding of REST APIs, webhooks, and third-party integrations
- Experience integrating AI models (OpenAI or similar)
- Experience with PostgreSQL or similar databases
- Experience with asynchronous processing (queues, workers)

Nice to have:
- Experience with automation systems
- Experience with financial or data-driven systems
- System architecture and scaling experience

Important:
This is NOT a simple website. This is a complex system that requires strong backend thinking and system design skills.

Looking for someone who can think at a system level, not just write code.

Full specification will be shared after initial discussion.