Add Chrome Web Store OAuth helper

[iFurySt]

Summary

• add a local loopback OAuth helper to generate the Chrome Web Store API refresh token
• expose it as pnpm chrome-web-store:oauth and include syntax checking in CI
• document how to generate CWS_REFRESH_TOKEN without committing secrets

Validation

• ./scripts/ci.sh
• pnpm chrome-web-store:oauth without credentials fails with a clear missing-client-id error
• git ls-files '*.md' | xargs pnpm dlx markdownlint-cli2
• git diff --check