ci: add BuildTool and route Android builds through it

DEVELOPMENT.md

@@ -2,6 +2,23 @@
 
 ## Build prerequisites
 
+Use the root build tooling so local builds and Gitea Actions run through the same script:
+
+```bash
+./BuildTool.sh --setup-only
+./BuildTool.sh --no-commit --apk-only
+./BuildTool.sh --no-commit --with-aab
+```
+
+Behavior summary:
+- `--setup-only` prepares the local Android SDK/tooling and exits.
+- `--apk-only` builds the debug APK.
+- `--with-aab` also builds the release AAB.
+- `--no-commit` skips the post-build git commit step.
+- Local builds increment `versionCode` and `versionName`.
+- CI can provide `CI_VERSION_CODE` to force the build version code and `CI_ARTIFACT_TIMESTAMP` to control the release AAB filename.
+- Artifacts are copied into `dist/`.
+
 - JDK 17
 - Android Studio (recommended)
 - Android SDK installed