Fullstack Developer/ Vibe Coder for SaaS Product

I have a HTML/CSS frontend prototype for a SaaS product (car photo editing tool). I need a developer to build the backend and make it fully functional. The core feature is: user uploads a photo, selects a background, API removes the background and composites the car onto the new scene + matches reflections/ shadows with AI, user downloads the result. I need auth, credit system, Stripe subscriptions, and the image processing pipeline built.