- Fetch list in js, if available
  - Fall back to rendering server-side if not
  - Use oojs-ui / OOUI for rendering form

This is mostly just Composer & Slim framework boilerplate.  There's a bit
of actual code in src/routes.php which uses davechild/textstatistics to
assign Dale-Chall readability scores to page intro extracts.

The need for a framework here at all is, of course, pretty questionable,
but then maybe we already know the initial use case is going to elaborate
rapidly.