Render page markdown

Markdown catch-all for LLM ingestion. Append `.md` to any storefront URL that resolves to a published blog content or a published page and the route returns the rendered Markdown body of that resource. Pages support locale prefixing (e.g. `/fr/about.md`). The route replies 404 when the path does not match an enabled, published resource, or when llms.txt is disabled on the site. The `path` parameter captures the full subpath after the site identifier and MUST end in `.md`; other shapes (32-hex `.txt` IndexNow keys) are matched by `/{key}` ahead of this route by route order.