Document the public API and CLI contract

[FU-max-boop]

Summary

• add a documentation index and complete handwritten reference for the supported Python and advanced evidence APIs
• document every CLI command, built-in scenario, exit code, and provider-free/network boundary
• add drift tests that keep the 24 + 17 exports, 7 commands, 4 scenarios, and documentation entry points synchronized

Validation

• 173 passed, 1 expected skip
• Ruff check and format check
• mypy src
• package build and Twine strict checks
• extracted minimal API example executed successfully and wrote a valid certificate

This changes documentation and drift coverage only; it does not change runtime behavior, schemas, CLI behavior, or public exports.