Update mermaid to v11 (with promises)

[mathpunk]

Have I ever made pull request to an open source repo? 🤔

I looked for all uses of this version of a Mermaid renderer and made 3 copies of that change. That duplication might not be desirable. Also it is LLM-enhanced code, you might not like the style or the error handling. But! I'll make any changes you like, or someone who has more mature maintainer skillz is welcome to build on this. The chat that led to my solution is here.

[mathpunk]

I should add, this is undertested: I don't know what the setup environment for base clerk is. I've always just cloned the clerk-demo and then hacked out the bits I don't need.

[mathpunk]

Hmmmm I restarted my machine and now it looks like I can only get v10 and earlier. There's something I must not understand about caching, either in my notebook or in jsdelivr. I'm hoping that the promise code is still helpful but I'm unclear how to fix the invalid module error I'm getting if I use something later than about 10.3.