Cross-Platform App With Authentication

I’m ready to turn my concept into a fully functioning mobile application that runs smoothly on both iOS and Android. The core build must include a solid email-and-password login flow with secure account creation, password reset, and session management. I’m flexible on the technical stack—whether you prefer Flutter, React Native, native Swift + Kotlin, or another proven approach—so long as you can ship a polished, stable experience on both platforms.

Here’s what I need from you:
• Complete front-end and back-end code for iOS and Android
• Robust email/password authentication, integrated with a scalable database
• Clear hand-off: source code, build instructions, and a brief walkthrough so I can maintain or expand the app later

If you have published cross-platform apps before and can demonstrate airtight login security, I’d like to see your work and discuss timelines.