chore(android): bump AGP to 8.9.1 and Java compatibility to 17

Transitive AndroidX dependencies (browser:1.9.0, core-ktx:1.17.0,
core:1.17.0) pulled in by the pub upgrade now require AGP 8.9.1+.

- AGP: 8.7.3 → 8.9.1
- Java source/target compatibility: 11 → 17
- Gradle 8.12 already satisfies AGP 8.9.1's minimum of 8.11.1

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

android/app/build.gradle.kts

@@ -24,12 +24,12 @@ android {
     ndkVersion = "27.0.12077973"
 
     compileOptions {
-        sourceCompatibility = JavaVersion.VERSION_11
-        targetCompatibility = JavaVersion.VERSION_11
+        sourceCompatibility = JavaVersion.VERSION_17
+        targetCompatibility = JavaVersion.VERSION_17
         isCoreLibraryDesugaringEnabled = true
     }
     kotlinOptions {
-        jvmTarget = JavaVersion.VERSION_11.toString()
+        jvmTarget = JavaVersion.VERSION_17.toString()
     }
 
     defaultConfig {

android/settings.gradle.kts

@@ -18,7 +18,7 @@ pluginManagement {
 
 plugins {
     id("dev.flutter.flutter-plugin-loader") version "1.0.0"
-    id("com.android.application") version "8.7.3" apply false
+    id("com.android.application") version "8.9.1" apply false
     id("org.jetbrains.kotlin.android") version "2.1.0" apply false
 }