movableink/studio-app — reverse-engineered prompt

Build me a small JavaScript package that acts as a base class for Studio apps. I want a StudioApp class that other developers can import, extend in their own index.js, then create in the browser and call render() on to display the app.

Keep it simple and reusable, like a clean foundation for custom apps rather than a full product. The main thing is that the base class should be easy to extend, export cleanly, and work with the usage where someone does class MyApp extends StudioApp {} and then new MyApp().render() from an HTML page.

Please include a minimal implementation, basic tests, and a short README that shows installation and the simple usage flow. If there are any obvious setup details needed to make it work nicely as a small library, handle those too. Look up current docs online if you need to, but keep the result lightweight and focused on the base app class.