💻 Convert low-res Soroban fee diagram to Mermaid

[JFWooten4]

The existing diagram isn't bad per se, but it is noticeably underscaled when expanding to wide viewframes. The text just gets huge inside the ref while the page looks minuscule by comparison. And going forward, it's a lot easier for anyone to update a code diagram than recreate the entire image.

[ElliotFriend]

Diagram is faithful to the fee model — nice work on this one.

there's a stray todo mermaid ! line (with trailing space) sitting at the tope of the page, which is what's breaking the mdx-format check. Remove that line and this is mergeable.

we might also consider labeling the fixed-component box "non-refundable resource fee" to match the section it links to.

i know this is also marked as a draft. let me know if it's still just a work-in-progress, too.

[JFWooten4]

All my drafts are WIPs, but I appreciate the feedback and ideas!

They're mostly to let others know what's being worked on, especially if they want to contribute (everything has edits by maintainers).

And yes, some of the old huge bulk ones are being slimmed down through more recent PRs, whereby they are my record of what's still to do.