Migrate docs from sphinx to docusaurus

[nebfield]

Since it's we use it on pgsc_calc, and markdown is nicer than rst

Autoapi needs to be replaced with:

https://pypi.org/project/pydoc-markdown/

• Migrate existing rst to markdown with an LLM
• Autoapi -> pydoc markdown
• Add HOWTOs for the new CLIs pgsc_calc load and pgsc_calc score