chore: prepare evals for public release

[stackbilt-admin]

Summary

• add the root Apache-2.0 license declared by the package
• add Node 20/22 CI for tests, build, and high-severity dependency audit
• upgrade Vitest from 2.x to 4.1.11
• remove the previous 7-advisory tree, including the critical Vitest UI advisory

Verification

• npm test — 10 tests passed on Vitest 4.1.11
• npm run build — passed
• npm audit --audit-level=high — 0 vulnerabilities

This prepares the repository for the separate operator decision to change visibility and publish @stackbilt/evals@0.2.0.