Add eslint and prettier

[sergeichestakov]

Why

We should definitely have eslint and prettier set up in this repo, esp now that Szymon and others are collaborating here more often, so that our formatting is consistent. I've been meaning to set this up just haven't gotten around to it until now.

Fixes WS-824

What changed

• Add eslint config which is as close as possible to our web config (minus custom rules, a11y/storybook other plugins we don't support, etc).
• Add prettier config which matches our web config (single quote strings, trailing comma, etc).
• Run lint fix on every file under src

Test plan

• CI / lint passes (run pnpm run lint locally)
• Config looks good
• App still works/starts/builds

[linear[bot]]

WS-824 Add eslint/prettier config