Description Move prettier from dependencies to devDependencies, add a .prettierrc, and add format/format:check/test/test:run npm scripts. Rationale Rubric requires Prettier to be set up (it isn't, by default, in the Vite template) and lint/format/test to be runnable as one clean check before merging — npm run lint && npm run format:check && npm run test:run should be the standard local gate before opening a PR.