Feature request: D2 diagram support

[ElenaBarmina-alation]

We're migrating docs from Astro/Starlight to Mintlify, and our diagrams are all in D2. Mintlify currently only renders Mermaid, so each D2 diagram either needs manual recreation or has to become a static image, losing the diagram-as-code workflow.

D2 is valuable to us for its layout engine and nested container support, which Mermaid doesn't replicate. Native D2 rendering, similar to the existing Mermaid support, would remove a real blocker for teams migrating from D2-supporting tooling.