feat: Update application ID and fix launcher icons for branding (had to convert jpg to png first)

android/app/build.gradle.kts

···
 
     defaultConfig {
         // TODO: Specify your own unique Application ID (https://developer.android.com/studio/build/application-id.html).
-        applicationId = "com.example.grain_flutter"
+        applicationId = "social.grain.grain_flutter"
         // You can update the following values to match your application needs.
         // For more information, see: https://flutter.dev/to/review-gradle-config.
         minSdk = flutter.minSdkVersion