bulletphysics/bullet3 ? reverse-engineered prompt

Build me the Bullet Physics SDK from this repo so I can run the example demos and try the Python bindings too. I want a clean local build on my machine, with the main C++ library compiling correctly, the example browser launching, and PyBullet available if that part is included in the build. If anything needs a small fix to make the build go through, please make it and explain what changed in simple terms.

Please also make sure there is an easy way to run one basic physics demo after build, and if the Python side is present, verify that I can import it and start a simple simulation. Look up the current build steps online if you need to, but keep the setup simple and practical.