feat: release signing,

fastlane metadata, CI workflow

.github/workflows/release.yml

@@ -0,0 +1,55 @@
+name: Release APK
+
+on:
+  push:
+    tags: ["v*"]
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: actions/setup-java@v4
+        with:
+          distribution: temurin
+          java-version: "17"
+
+      - uses: subosito/flutter-action@v2
+        with:
+          flutter-version: "stable"
+          cache: true
+
+      - name: Extract version code from pubspec
+        run: |
+          VERSION=$(grep '^version:' pubspec.yaml | sed 's/version: //')
+          VERSION_CODE=$(echo "$VERSION" | grep -oP '(?<=\+)\d+')
+          VERSION_NAME=$(echo "$VERSION" | grep -oP '^[^+]+')
+          echo "VERSION_CODE=$VERSION_CODE" >> $GITHUB_ENV
+          echo "VERSION_NAME=$VERSION_NAME" >> $GITHUB_ENV
+
+      - name: Decode keystore
+        run: |
+          echo "${{ secrets.KEYSTORE_BASE64 }}" | base64 -d > android/app/kirakira-release.jks
+          echo "KEYSTORE_PATH=$GITHUB_WORKSPACE/android/app/kirakira-release.jks" >> $GITHUB_ENV
+
+      - name: Build release APK (prod flavor)
+        env:
+          STORE_PASSWORD: ${{ secrets.STORE_PASSWORD }}
+          KEY_ALIAS:      ${{ secrets.KEY_ALIAS }}
+          KEY_PASSWORD:   ${{ secrets.KEY_PASSWORD }}
+        run: flutter build apk --release --flavor prod
+
+      - name: Rename APK
+        run: |
+          cp build/app/outputs/flutter-apk/app-prod-release.apk \
+             "kirakira-${{ env.VERSION_NAME }}.apk"
+
+      - name: Create GitHub Release
+        uses: softprops/action-gh-release@v2
+        with:
+          files: kirakira-*.apk
+          body_path: fastlane/metadata/android/en-US/changelogs/${{ env.VERSION_CODE }}.txt
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}