Set up your machine

Android development needs one big tool and a couple of small ones, all free, on Mac, Windows, or Linux:

Android Studio — Google's IDE. It bundles the Kotlin compiler, the Android SDK, and the emulator (a virtual Android phone that runs on your computer). It's a big download, so start it first.
A Pixel emulator (API 36) — Android Studio creates this for you; no physical phone required.
Gradle — the build tool. You never install it by hand: opening the project in Android Studio downloads the exact version pinned in this repo and syncs automatically.

The backend also needs uv (a fast Python package manager) — one install command and you're done.