mermaid export

[matt-beanland]

legacy graph style
nodes should be round
include title
support export from the Artefact, and add to export ArtefactKino pane.

• wired the title through, including screen reader for accessibility
• raise a card description

[matt-beanland]

There is also the possibility of rendering mermaid live in ArtefactKino. There is likely a MermaidKino in any case.