Render repo Markdown to standalone HTML with GitHub's own renderer

To preview or ship a README as a standalone page that matches github.com, POST it to GitHub's markdown API: gh api -X POST /markdown --input body.json, with body {"text": <markdown>, "mode": "markdown"}. Use mode "markdown" rather than "gfm": gfm renders the way comments do, so every hard-wrapped source line turns into a <br>, while "markdown" joins wrapped lines the way repo file views do. Relative <img src> paths come back unchanged, so the HTML works next to its images. Wrap the output in <article class="markdown-body"> with the github-markdown-css stylesheet. Playwright MCP blocks file:// URLs, so serve the folder with python3 -m http.server to screenshot it; its single thread can reset a few parallel image requests, which isn't a page bug.