feat: check examples

[rich-iannone]

This PR adds great-docs check-examples, which executes every Python code cell across your documentation pages and docstring examples, reporting which ones succeed and which error (catching broken examples). It respects Quarto's existing conventions like #| error: true and #| eval: false, and provides page- and cell-level opt-outs for cases where checking doesn't apply. Results are shown with per-section progress bars, console output with pass/fail detail, and optional JSON output for CI integration.

[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 34359622988

# or always the latest build for this PR
great-docs preview --pr 346

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.