Swaps mocha-headless-chrome and elmish-testing-library for a very basic playwright wrapper

[ddellacosta]

Alright as of 2026-03-23 this is effectively working in terms of a "hello world" implementation--Playwright is running and I can toggle off headless mode and see the browser pop up with the code running.

Todo:

• get the websocket stuff implemented
• get a page loading via data fed in with the websocket implementation
• get current Test.Main assertions/tests working
• get fixtures that load in groups going and tests written that exercise the groups (optional?)
• figure out how this is going to run in CI, including standing up a little web server to serve the index page (?)
• allure report compatibility (probably could be lumped in with the item above, but I realized this is going to be involved, sadly)
• update README
• ...what else?