playcanvas/engine ? reverse-engineered prompt

Build me an open source JavaScript game engine for the browser, similar to PlayCanvas. I want people to be able to make interactive 3D apps, games, and visualizations that run on phones, tablets, and desktop browsers.

It should have a simple developer experience where someone can install it, create a canvas, add a cube, camera, light, and start the app with a few lines of code. Include support for WebGL2, WebGPU where available, loading glTF assets, basic 3D rendering, animation, input from mouse, touch, keyboard, and gamepads, positional sound, and WebXR for AR and VR. Also include room for physics and Gaussian splat rendering.

Please set up the npm project, source code, build scripts, TypeScript types, examples, and tests. Add a clear README with install instructions and a spinning cube example. Look up current browser graphics docs online if you need to.