Mojo Python Interop

If you're calling Python libraries from Mojo or building Python extension modules in Mojo, this skill keeps you from fighting with outdated syntax. The main thing it hammers home is the `py=` keyword requirement for PythonObject conversions (Int(py=obj), not Int(obj)), which pretrained models consistently get wrong. It also covers PythonModuleBuilder patterns for exposing Mojo structs to Python, including the two method signature styles for downcasting. The skill is terse by design since it's meant as a correction layer, not a tutorial. Use it alongside mojo-syntax when your Mojo code needs to talk to Python in either direction.