build: Bump Android Gradle Plugin to 8.9.1

fix(chat): Improve Markdown formatter state management

- Explicitly clear the streaming formatter when switching conversations to prevent state leakage.
- Implement defensive checks to ensure the formatter is always associated with the correct message, resetting it if a mismatch is detected.
- Refine the formatter seeding logic to only use existing content in resume scenarios, preventing content duplication.
- Add detailed logging to the chat provider for better debugging of streaming and formatter behavior.

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
 }