Namespace graph schema with Py and PY_ prefixes for multi-language coexistence

[rahlk]

Rename the console command from codeanalyzer to canpy, paralleling the
TypeScript backend's cants. The PyPI package (codeanalyzer-python) and the
importable codeanalyzer module are unchanged.

Scope:

• pyproject [project.scripts]: canpy entry point
• Typer app name
• README, CHANGELOG, installer, and release workflow references