## Summary
This is prep-work for the Red Knot playground. We'll have two
playgrounds, one for Red Knot and Ruff.
I want to share some components between the two, a "shared" NPM package
in a local workspace is a great fit for that.
I also want to share the dev dependencies and dev scripts. Again, NPM
workspaces are great for that.
This PR also sets up a CI workflow for the playground to prevent
surprises during the release.
## Test Plan
CI, local `npm install`, `npm start`, ...
I verified that the new CI step fails if there's a typescript or
formatting error.
* [Deployment test
run](https://github.com/astral-sh/ruff/actions/runs/13904914480/job/38905524353)
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