- Bump AGP to 9.3.1 (from 8.11.1) and the example app's Gradle wrapper to
  9.6.1 to satisfy AGP 9.3's minimum Gradle requirement.
- android/build.gradle now only applies the standalone Kotlin Gradle Plugin
  when built-in Kotlin isn't active (older AGP, or no opt-in via the
  android.builtInKotlin Gradle property), matching the pattern other
  actively-maintained plugins (e.g. file_picker) use so the plugin keeps
  building under both older and newer AGP. Verified with a real
  `flutter build apk --debug` against the example app.
- Loosen the jni_flutter dependency from an exact pin to ^1.0.1.
- Add native_pdf_engine to the Pub.dev publish workflow's package matrix.