Add CI

[wwall3r]

Should run:

• pnpm i and cache
• pnpm lint
• pnpm create-types-check and then ensure git diff of src/lib/db/types.ts is empty
• pnpm check
• any unit tests (via vitest)
• pnpm build
• integration tests (probably via https://github.com/marketplace/actions/supabase-cli-action and running supabase init; supabase start; pnpm preview)
• db tests (via supabase test db)
• if everything passes and on master, deploy to production? Or potentially leave that as a separate, manual action.