Mermaid

Mermaid diagrams are drawn in the browser, and the library is loaded only when a deck has one. Options come after the language:

```mermaid {theme:'neutral', scale:0.8}
graph TD
A[Text] --> B{Decision}
```

• theme defaults to dark or default, following the colour mode.
• Any other key is passed to Mermaid's own initialize.
• <slide-ng-mermaid code="..." /> works as a tag too.
• While a diagram is being drawn its element has data-slide-ng-waitfor, and the attribute goes away when the picture is there. The exporter waits for it.

A setup/mermaid.ts file returns Mermaid's config for every diagram. See Setup hooks.