signalapp/signal-android — reverse-engineered prompt

Build me an Android app for private messaging, similar to Signal. I want a clean simple messenger where people can sign up with their phone number, find contacts, send and receive secure high quality text messages over WiFi or mobile data, and make clear voice and video calls.

Privacy should be the main point, so conversations should feel protected by default and the app should not make users hunt through settings to turn safety on. Include the basic screens a real user expects, welcome and setup, chat list, one to one conversation, contact picker, call screen, settings, and helpful empty states.

Keep the interface calm and fast, with notifications and sensible error messages when the network is unavailable. Use Kotlin for Android and set it up so it can be built and run locally. If any security or calling details need current best practices, look up the latest Android docs and use a reasonable safe implementation rather than fake UI only.