restart_app 1.9.1

Fixes the AGP 9 build failure in 1.9.0. Projects generated by Flutter 3.44 and later use Android Gradle Plugin 9 with android.builtInKotlin=false, and 1.9.0 left that combination with no Kotlin plugin at all, so evaluation failed with Could not find method kotlin(). Upgrading is enough; no app-side change is needed.

• Fixed the Android build failing on AGP 9 with Could not find method kotlin(), which hit every project generated by Flutter 3.44 and later (#56)
• Changed how the plugin decides to apply the Kotlin Gradle Plugin: it now checks whether Kotlin has already been provided instead of reading the AGP major version, so AGP 9 with android.builtInKotlin=false gets a Kotlin toolchain like every other combination
• Kept the Android namespace unconditional now that every supported AGP requires it
• Added a CI job that builds a fresh app against AGP 9.0 and AGP 9.1 on their matching Gradle versions

Verified on AGP 8.6, 8.11, 9.0.1, 9.1.0 and 9.3.1, on Flutter 3.44 and 3.47, with built-in Kotlin both off and on.