fix: refinements MCP index page

[rich-iannone]

This PR focuses on improving the handling and presentation of reference index pages (API, CLI, and MCP) in the documentation system, along with minor docstring and style updates. The changes ensure that reference index pages are properly identified via a new CSS class, which allows for more precise styling and behavior (such as hiding the copy-page widget on these indexes).

[github-actions]

📚 Preview this PR's docs locally

Fetch the just-built site and open it in your browser:

# this exact build
great-docs preview --run 31497179015

# or always the latest build for this PR
great-docs preview --pr 316

Auth & tips

• Requires great-docs: pip install great-docs (or run via pipx/uvx).
• Auth: run gh auth login then add --use-gh, or set GITHUB_TOKEN (needs Actions: read).
• Jump to a page: add --path reference/index.html.
• Latest vs exact: --pr <n> grabs the newest build; --run <id> pins this one.
• Re-download: --refresh ignores the local cache.