android: keyboard height tracking via JNI/FFI bridge

- C bridge (keyboard_bridge.c) stores keyboard state in globals.
  Kotlin writes via JNI, Dart reads via FFI — zero async delay,
  same architecture as iOS.
- WindowInsetsAnimation.Callback tracks open/close per-frame.
- OnGlobalLayoutListener catches silent height changes (emoji
  keyboard resize, floating keyboard toggle).
- Dart animation replay stays iOS-only; Android reads native
  per-frame values directly.
- Cleaned up old Java stub, updated build.gradle for Kotlin + CMake
  with 16KB page alignment (Android 15+).
- Example app rewritten to demonstrate UxKeyboard usage.

android/build.gradle

@@ -2,33 +2,53 @@ group 'io.swipelab.ux'
 version '1.0-SNAPSHOT'
 
 buildscript {
+    ext.kotlin_version = '1.9.22'
     repositories {
         google()
-        jcenter()
+        mavenCentral()
     }
 
     dependencies {
-        classpath 'com.android.tools.build:gradle:3.2.1'
+        classpath 'com.android.tools.build:gradle:8.1.0'
+        classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version"
     }
 }
 
 rootProject.allprojects {
     repositories {
         google()
-        jcenter()
+        mavenCentral()
     }
 }
 
 apply plugin: 'com.android.library'
+apply plugin: 'kotlin-android'
 
 android {
-    compileSdkVersion 28
+    namespace 'io.swipelab.ux'
+    compileSdk 34
 
     defaultConfig {
-        minSdkVersion 16
-        testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
+        minSdk 21
+        externalNativeBuild {
+            cmake {
+                cppFlags ""
+            }
+        }
     }
-    lintOptions {
-        disable 'InvalidPackage'
+
+    externalNativeBuild {
+        cmake {
+            path "src/main/jni/CMakeLists.txt"
+        }
+    }
+
+    compileOptions {
+        sourceCompatibility JavaVersion.VERSION_1_8
+        targetCompatibility JavaVersion.VERSION_1_8
+    }
+
+    kotlinOptions {
+        jvmTarget = '1.8'
     }
 }