Adds .forgejo/workflows/ with two workflows that run on the self-hosted
vega-runner (Forgejo act_runner with Nix support):
- build-fdroid-debug.yml: builds fdroidDebug variant (no Firebase)
- build-play-debug.yml: builds playDebug variant (with Firebase)
Both install the Android SDK via command-line tools, set up JDK 21,
cache Gradle, build the APK, and upload artifacts.
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
