feat(build): migrate to declarative Gradle plugin DSL and bump Dart SDK constraint to >=3.0.0 <4.0.0

android/app/build.gradle

@@ -1,3 +1,10 @@
+plugins {
+    id "com.android.application"
+    id "kotlin-android"
+    id "dev.flutter.flutter-gradle-plugin"
+    id "com.google.gms.google-services"
+}
+
 def localProperties = new Properties()
 def localPropertiesFile = rootProject.file('local.properties')
 if (localPropertiesFile.exists()) {
@@ -6,11 +13,6 @@ if (localPropertiesFile.exists()) {
     }
 }
 
-def flutterRoot = localProperties.getProperty('flutter.sdk')
-if (flutterRoot == null) {
-    throw new GradleException("Flutter SDK not found. Define location with flutter.sdk in the local.properties file.")
-}
-
 def flutterVersionCode = localProperties.getProperty('flutter.versionCode')
 if (flutterVersionCode == null) {
     flutterVersionCode = '1'
@@ -21,13 +23,6 @@ if (flutterVersionName == null) {
     flutterVersionName = '1.0'
 }
 
-apply plugin: 'com.android.application'
-// START: FlutterFire Configuration
-apply plugin: 'com.google.gms.google-services'
-// END: FlutterFire Configuration
-apply plugin: 'kotlin-android'
-apply from: "$flutterRoot/packages/flutter_tools/gradle/flutter.gradle"
-
 android {
     namespace "com.oggauergemeindetrommler.app"
     compileSdkVersion flutter.compileSdkVersion
@@ -75,6 +70,4 @@ flutter {
     source '../..'
 }
 
-dependencies {
-    implementation "org.jetbrains.kotlin:kotlin-stdlib-jdk7:$kotlin_version"
-}
+dependencies {}

android/build.gradle

@@ -1,18 +1,3 @@
-buildscript {
-    ext.kotlin_version = '1.9.22'
-    repositories {
-        google()
-        mavenCentral()
-    }
-
-    dependencies {
-        classpath 'com.android.tools.build:gradle:8.5.2'
-        // START: FlutterFire Configuration
-        classpath 'com.google.gms:google-services:4.4.1'
-        // END: FlutterFire Configuration
-        classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version"
-    }
-}
 
 allprojects {
     repositories {

android/settings.gradle

@@ -1,11 +1,30 @@
-include ':app'
+pluginManagement {
+    def flutterSdkPath = {
+        def properties = new Properties()
+        def localPropertiesFile = file("local.properties")
+        if (localPropertiesFile.exists()) {
+            localPropertiesFile.withInputStream { properties.load(it) }
+        }
+        def flutterSdkPath = properties.getProperty("flutter.sdk") ?: System.getenv('FLUTTER_ROOT') ?: System.getenv('FLUTTER_HOME')
+        assert flutterSdkPath != null, "flutter.sdk not set in local.properties or FLUTTER_ROOT environment variable"
+        return flutterSdkPath
+    }
+    settings.ext.flutterSdkPath = flutterSdkPath()
 
-def localPropertiesFile = new File(rootProject.projectDir, "local.properties")
-def properties = new Properties()
+    includeBuild("${settings.ext.flutterSdkPath}/packages/flutter_tools/gradle")
 
-assert localPropertiesFile.exists()
-localPropertiesFile.withReader("UTF-8") { reader -> properties.load(reader) }
+    repositories {
+        google()
+        mavenCentral()
+        gradlePluginPortal()
+    }
+}
 
-def flutterSdkPath = properties.getProperty("flutter.sdk")
-assert flutterSdkPath != null, "flutter.sdk not set in local.properties"
-apply from: "$flutterSdkPath/packages/flutter_tools/gradle/app_plugin_loader.gradle"
+plugins {
+    id "dev.flutter.flutter-plugin-loader" version "1.0.0"
+    id "com.android.application" version "8.5.2" apply false
+    id "org.jetbrains.kotlin.android" version "1.9.22" apply false
+    id "com.google.gms.google-services" version "4.4.1" apply false
+}
+
+include ":app"