Fix docs formatting for mkdocs rendering

[thomas-bartlett]

Fixes table and code block formatting issues in the custom rules documentation. Uses indented code blocks for proper list nesting and shortens table content to prevent column wrapping.

[Copilot]

Pull request overview

This PR updates the MkDocs configuration and custom rules documentation so that the "Custom Rules" page is visible in the navigation and renders correctly in MkDocs/Material, with better list-nested code blocks and a more compact frontmatter schema table.

Changes:

• Add the Custom Rules page to the MkDocs navigation so it appears in the site sidebar.
• Reformat the Quick Start section code examples in docs/custom-rules.md to use indented code blocks that nest correctly under ordered list items.
• Simplify and align the frontmatter schema table, shortening the tags description and pointing readers to src/tag_mappings.py to avoid column wrapping.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
mkdocs.yml	Adds a Custom Rules entry to the navigation, wiring the new/updated documentation page into the docs site.
docs/custom-rules.md	Adjusts Markdown formatting (indented code blocks and table alignment/wording) for correct MkDocs rendering and clearer linkage to the tag mappings source.

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[ramraaj25]

Looks good to me! Thanks