Function renderMarkdownToHtml

Convert the Markdown body to sanitised HTML.

Pipeline stages

1. preprocessMermaidFences — \``mermaid→

   `
   remark-parse + remark-gfm — parse markdown (incl. GFM tables / task lists / strikethrough)
   remark-rehype with allowDangerousHtml: true — preserve the <pre class="mermaid"> wrappers
   rehype-raw — re-parse the preserved raw HTML into the HAST tree
   rehypeSlugWithPrefix — inject stable, rm--prefixed id= attributes on every heading
   rehype-autolink-headings — append an anchor <a> child to every heading for deep-linking (behavior: 'append')
   rehypeWrapTables — wrap <table> in <div class="rm-table-wrap">
   rehype-sanitize with sanitizeSchema — scrub anything not in the allow-list
   rehype-stringify — serialise HAST → HTML with allowDangerousHtml: false