Drop setup-java, setup-android and the Gradle wrapper in favour of the
flake's pinned JDK, Gradle and Android SDK, restoring the Nix store with
cache-nix-action, so the release and next builds share the dev toolchain.
Commit a public debug keystore and point the debug signing config at it,
and add a next build type (release-like, same key). Both carry the .next
application id, so next builds install alongside the release and update
each other without exposing the release key. A GitHub workflow builds
both APKs on every push to main and uploads them as artifacts.
austinried