Drop Node.js 16 from CI matrix

[nev21]

Summary

Node.js 16 runs in the CI matrix but is no longer supported by dependencies.

Details

• Several dependencies (such as puppeteer, @pnpm/error) now require at least Node.js 18.
• The CI job fails on Node 16 due to unsupported engine and lack of native structuredClone.
• Node.js 16 is now End-of-Life.

Solution

• Remove Node.js 16 from the matrix in .github/workflows/ci.yml.
• Document this change in the changelog as a breaking CI/tooling change, if needed.

References

• Job failure log