docs: refresh public release status

[daichunghy]

Summary

• refresh the README status date to 2026-08-30
• point the portfolio link at the current 2026-08-28 audit
• keep the beta.5, unpublished npm package, and no-adoption boundaries explicit

Verification

• npm run verify passes from origin/main with the README change
• GitHub release, repository metrics and npm package state were checked live before editing

This is a documentation-only update. It does not change release or package visibility.