Introduce an API endpoint that serves preprocessed Markdown for guide pages (.mdx) and a client "Copy as Markdown" button. Adds mdxToMarkdown transformer to convert MDX/JSX (admonitions, Image, other components) into plain Markdown, a test script to scan guides for unhandled JSX, and a CopyMarkdownButton client component. Integrates the copy button into GuidesMdx template and GuidesTableOfContents (TOC now accepts children), updates next.config.mjs with rewrites and outputFileTracingIncludes for the new API, and adds a navigation types reference in next-env.d.ts. The API enforces existing access checks via getGuidesMarkdown and returns Markdown with caching headers.