chore(android): upgrade toolchain to AGP 8.13.1 / Kotlin 2.3.0 (#23)

Bump Android Gradle Plugin from 8.11.1 to 8.13.1 and Kotlin from
2.2.20 to 2.3.0 to align with newer plugin version requirements.

Kotlin 2.3.0 removed the kotlinOptions DSL free-string assignment.
Migrate to the compilerOptions DSL for JVM target configuration.

Gradle wrapper remains at 8.14 (compatible with AGP 8.13.1).

apps/chanora_flutter/android/settings.gradle.kts

@@ -19,8 +19,8 @@ pluginManagement {
 
 plugins {
     id("dev.flutter.flutter-plugin-loader") version "1.0.0"
-    id("com.android.application") version "8.11.1" apply false
-    id("org.jetbrains.kotlin.android") version "2.2.20" apply false
+    id("com.android.application") version "8.13.1" apply false
+    id("org.jetbrains.kotlin.android") version "2.3.0" apply false
 }
 
 include(":app")