fix: enable core library desugaring for flutter_local_notifications

flutter_local_notifications 插件依赖 java.time API，需要启用 Android core
library desugaring 才能在低版本设备上运行。

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

it0_app/android/app/build.gradle.kts

@@ -11,6 +11,7 @@ android {
     ndkVersion = flutter.ndkVersion
 
     compileOptions {
+        isCoreLibraryDesugaringEnabled = true
         sourceCompatibility = JavaVersion.VERSION_17
         targetCompatibility = JavaVersion.VERSION_17
     }
@@ -39,6 +40,10 @@ android {
     }
 }
 
+dependencies {
+    coreLibraryDesugaring("com.android.tools:desugar_jdk_libs:2.1.4")
+}
+
 flutter {
     source = "../.."
 }