Publish releases to npm from GitHub Actions

[devmaxxx]

Summary

• Add .github/workflows/release.yml: on a published GitHub release (or a manual run), lint, build, typecheck and unit-test, check the tag matches package.json and the version is not on npm yet, then npm publish through Trusted Publishing (OIDC, provenance, no token or OTP). Prereleases go to the next dist-tag.
• Document the release steps in the README.

Needs a one-time Trusted Publisher entry on npmjs.com (package settings → GitHub Actions → devmaxxx / react-clear-browser-cache / release.yml).

Test plan

• After the npm setting, run the workflow by hand on master to publish 1.0.0