Renders a structured diagram module into a Mermaid.js string representation.

Mermaid is a JavaScript-based diagramming tool supported natively in GitHub, GitLab, Notion, and many other platforms.

Supported diagram types

All Choreo diagram modules implement this protocol:

mermaid = Choreo.to_mermaid(system)

The output can be embedded in Markdown:

```mermaid
<%= mermaid %>
```