Cross-Platform Mobile App Build -- 2

I want to turn an existing concept into a fully working mobile application released on both the App Store and Google Play. The scope covers everything from initial technical planning through design, coding, testing, and store submission, with clean, well-documented source code handed over at the end.

Key expectations
• Universal build for iOS and Android (native Swift/Kotlin or a solid cross-platform framework such as Flutter or React Native—feel free to propose what serves performance and future maintenance best).
• Modern, intuitive UI that follows Apple Human Interface Guidelines and Material Design where appropriate.
• Smooth onboarding, secure user authentication, and a lightweight backend connection (REST or GraphQL) ready for scaling.
• Comprehensive QA on real devices, plus TestFlight / internal testing setup.
• Final deliverables: compiled binaries, full source, build instructions, and live listings in both stores.

Please outline your proposed tech stack, a rough milestone breakdown, and any similar apps you have shipped so we can move straight into scheduling.