Update the site directory. This is partly in anticipation of adding the Leios visualizer to the site, and partly because dependabot is complaining about it.

• Run yarn upgrade to update all dependencies to latest patches (without violating semver restrictions in package.json)
• Replace JSX.Element type annotations with React.ReactElement. It's the same type, but VSCode understands the automatic React import better than the automatic JSX import.
• Update the node engine from 18 to 22. Node 18 goes EOL this month, Node 22 is LTS (until later this month), and a dependency was complaining about the node engine being too old.

Tested on my machine and it was fine.