One-Screen Flutter Subscription App

I need a very lean Flutter project that does just three things:

1. launches a single, clean screen on both iOS and Android,
2. lets the user sign up or log in with email + password, and
3. offers a yearly renewable subscription processed natively through Google Play Billing and Apple StoreKit.

The UI can be minimal—think logo, short pitch, a “Subscribe” button, and a small sign-in / sign-up area. I’m happy for you to use the standard in_app_purchase package (or another proven solution) and Firebase Authentication, provided the flow feels native and the purchase is properly validated and restorable on both stores.

Deliverables
• Full Flutter source code, ready to open in the current stable channel
• Working builds (or TestFlight / internal test) that demonstrate sign-in and a successful yearly purchase on each platform
• Clear setup notes so I can swap in my own store IDs, bundle IDs, and branding
• Brief instructions on testing, restoring, and cancelling the subscription during review

Keep the project tight and straightforward—no extra screens, no extra plans.