Add auto-generated API reference

[jtdub]

Description

The project has no single API reference page. API documentation is currently scattered across multiple doc files (utilities.md, drivers.md, remediation-reporting.md). The project already has py.typed, strict type annotations, and comprehensive Pydantic models — all the ingredients for excellent auto-generated docs.

Proposed Improvement

Add an auto-generated API reference using one of:

• mkdocstrings (integrates with the existing mkdocs setup)
• pdoc (zero-config, generates from type annotations)

This would provide a single place for users to look up all public classes, methods, and their signatures without reading source code.

The existing mkdocs site (mkdocs.yml) could add an "API Reference" nav entry that auto-generates from the hier_config package.