How to migrate a Flutter add-to-app module into a standalone Flutter app

### Use case

We have been using Flutter as an add-to-app module inside our existing native iOS/Android project.
After several iterations, most of our app’s functionality now lives inside this Flutter module.

We now want to migrate this Flutter add-to-app module into a standalone Flutter application (pure Flutter app).
However, there is currently no clear documentation or recommended process on how to do this migration.

We couldn’t find any package on pub.dev that addresses this use case.

### Proposal

Please provide official documentation, guidance, or tooling on how to convert a Flutter add-to-app module into a standalone Flutter application, including potential pitfalls for Android/iOS build configurations, dependencies, and plugins.

This would help teams that started with add-to-app and later want to fully migrate to Flutter.