Add CI workflow to auto-build and release signed APKs

Builds a signed release APK and publishes it as a GitHub Release
whenever a v*.*.* tag is pushed, using the keystore/passwords stored
as repo secrets.

Author: roman-gmk

.github/workflows/release.yml

@@ -0,0 +1,50 @@
+name: Release
+
+on:
+  push:
+    tags:
+      - 'v*.*.*'
+
+permissions:
+  contents: write
+
+jobs:
+  build-and-release:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Set up JDK 17
+        uses: actions/setup-java@v4
+        with:
+          distribution: temurin
+          java-version: '17'
+
+      - name: Set up Android SDK
+        uses: android-actions/setup-android@v3
+
+      - name: Decode keystore
+        run: echo "${{ secrets.KEYSTORE_BASE64 }}" | base64 -d > release.jks
+
+      - name: Write key.properties
+        run: |
+          cat > key.properties <<EOF
+          storePassword=${{ secrets.KEYSTORE_PASSWORD }}
+          keyPassword=${{ secrets.KEY_PASSWORD }}
+          keyAlias=${{ secrets.KEY_ALIAS }}
+          storeFile=../release.jks
+          EOF
+
+      - name: Build signed release APK
+        run: ./gradlew assembleRelease
+
+      - name: Rename APK
+        run: cp app/build/outputs/apk/release/app-release.apk SleepButton-${{ github.ref_name }}.apk
+
+      - name: Create GitHub release
+        uses: softprops/action-gh-release@v2
+        with:
+          name: Sleep Button ${{ github.ref_name }}
+          files: SleepButton-${{ github.ref_name }}.apk
+          generate_release_notes: true