iOS App Build From Script

I already have a detailed script that maps out every screen and interaction for the app; what I’m missing is the actual build and a full UI/UX treatment. The goal is simple: launch a native iOS app whose core value revolves around a backend-driven user subscription system. Users should be able to create an account, select a plan, and retain access only while their subscription is active, with the entire flow handled through Apple’s in-app purchase framework.

Here’s what I need you to take ownership of:
• Translate the script into clean, well-structured Swift code, fully tested and ready for TestFlight.
• Design the complete interface from scratch—layouts, icons, animations, onboarding, dark/light mode, and all micro-interactions—so it feels perfectly at home on every modern iPhone or iPad.
• Connect the frontend to a secure backend that manages sign-up/sign-in, subscription status, and gated content (Firebase, Supabase, or a stack you recommend).
• Implement StoreKit-based in-app purchases to start, renew, and restore subscriptions seamlessly.
• Hand over the Xcode project, editable design files (Figma, Sketch, or XD), and a TestFlight build that mirrors the script’s flow without crashes.

Acceptance criteria: the TestFlight build must match the script line-for-line, subscriptions must activate and expire correctly, and the interface should meet Apple’s HIG for a smooth review.

If you’ve shipped subscription apps before, please mention them along with a rough timeline and your preferred toolchain. I’m also open to your ideas on push notifications or other engagement touches that could enhance retention.