💻 Replace mermaid clawback img with code

[JFWooten4]

This converts the PNG screenshot of a Mermaid diagram in #1828 to a Mermaid diagram. That should make it a lot easier to split it up, reproduce, and scale to finish #870 (comment) while working ✨ in dark mode 🤩

[ElliotFriend]

The diagram content checks out against the worked example in clawbacks.mdx, and dropping the PNG is fine (nothing else references it).

The MDX is currently malformed, which is why mdx-format fails: the closing fence has four backticks, there's no blank line between <summary> and the opening fence, and the node definitions got smashed onto the subgraph lines (looks like a formatter pass mangled it). Fix those three and the diagram should render — ready to merge after that.