Android: reproducible signed build (keystore and Bazaar RSA key read from outside the repo), Gradle wrapper, build-apk.sh

First time the project has been built: debug and release both produce an APK.
Release refuses to build without keystore or RSA key.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

android/.gitignore

@@ -6,3 +6,4 @@ local.properties
 *.iml
 *.jks
 *.keystore
+build-out/