Deliver Android 16-compatible signed release APK in-repo

[Copilot]

This PR updates the Android app release pipeline and artifacts so the repository now includes a compiled, signed APK targeting Android 16 compatibility.

• Android 16 target alignment

  • compileSdk and targetSdk were raised to 36 in app module build config.
  • Added android.suppressUnsupportedCompileSdk=36 to keep builds stable with current AGP.

• Release signing configuration

  • Added an explicit release signing config and wired it into the release build type.
  • Added a repository-tracked keystore used for generating a signed release APK.

• Build reproducibility + artifact delivery

  • Restored gradle/wrapper/gradle-wrapper.jar so ./gradlew works in clean environments.
  • Updated ignore rules to allow committing release artifacts/required signing assets.
  • Added signed output artifact at:
    • release-apk/OpenWith-SaveAs-android16-signed.apk

android {
    compileSdk 36
    defaultConfig { targetSdk 36 }

    signingConfigs {
        release {
            storeFile file("release-keystore.jks")
            storePassword "android"
            keyAlias "release"
            keyPassword "android"
        }
    }

    buildTypes {
        release {
            signingConfig signingConfigs.release
        }
    }
}