chore: extend Prettier to docs, config, scripts and examples #16

The format/format:check scripts only cover src/**/*.{ts,tsx} and tests/**/*.{ts,tsx}. Running Prettier over the rest of the repo shows several files are not formatted, e.g. .eslintrc.cjs, scripts/benchmark.ts, examples/node-esm.mjs (README.md and the community files were formatted in #11).

A .prettierignore already excludes generated files (CHANGELOG.md, dist, coverage, docs/dist, lockfiles).

What to do

1. Widen the globs in package.json, e.g. prettier --write . / prettier --check . (relying on .prettierignore), or explicit globs for *.{md,json,yml,cjs,mjs,ts}, scripts/, examples/ and .github/.
2. Run npm run format once and commit the result (formatting-only diff).
3. Make sure npm run format:check passes and nothing generated (CHANGELOG, docs/dist/output.css) gets reformatted.

PR title: chore: format docs, config, scripts and examples with Prettier.