build: add script to build android locally

docker/build-android-local.sh

@@ -0,0 +1,21 @@
+#!/bin/bash
+set -euo pipefail
+
+SCRIPT_DIR="$(dirname "$(realpath "${BASH_SOURCE[0]}")")"
+PROJECT_ROOT="$(dirname "$SCRIPT_DIR")"
+IMAGE_NAME="mumble-web2/android-release-builder:local"
+
+TARGET="${1:-aarch64-linux-android}"
+
+echo "==> Building Android builder Docker image..."
+docker build -t "$IMAGE_NAME" -f "$SCRIPT_DIR/android-release-builder.Dockerfile" "$PROJECT_ROOT"
+
+echo "==> Building Android APK (target: $TARGET)..."
+docker run --rm \
+    -v "$PROJECT_ROOT:/app" \
+    -w /app \
+    "$IMAGE_NAME" \
+    dx build --platform android --target "$TARGET" --release -p mumble-web2-gui
+
+echo "==> Done! APK should be at:"
+echo "    target/dx/mumble-web2-gui/release/android/app/app/build/outputs/apk/debug/app-debug.apk"