ci: add Node.js runtime matrix coverage

[nensii21]

Summary

• Add a lightweight CI matrix for Node.js runtime validation
• Run frontend checks on Node.js 20 and 22
• Document CI-validated runtime baselines in the README
• Keep the matrix small and maintainable

Motivation

The project documentation states support for Node.js 20+. Previously, CI exercised only a single Node.js runtime version. This change adds coverage for multiple supported Node.js baselines so runtime support claims are backed by automation.

Changes

CI

Updated the frontend-checks job to use a Node.js version matrix:

• Node.js 20
• Node.js 22

Documentation

Added a Runtime Support section describing the runtime baselines currently validated by CI.

Testing

• Verified workflow configuration changes
• Frontend checks now execute on Node.js 20 and Node.js 22
• Existing job structure remains unchanged to keep CI maintainable

[nensii21]

The Node.js matrix jobs completed successfully, but the required frontend-checks status remains in an Expected state.

This appears to be due to branch protection expecting a single frontend-checks check while the workflow now reports matrix jobs for Node.js 20 and 22.

Would you prefer:

• updating the required status checks to the matrix job names, or
• adding a non-matrix aggregation job (similar to backend-tests) that preserves the existing frontend-checks required check name?

[utksh1]

This overlaps heavily with #673 for the backend test split, and the README addition currently duplicates the Runtime Support heading. Please rebase on latest main, remove the duplicated backend split if #673 lands first, and keep this PR focused on the Node runtime matrix plus a single clean README runtime-support note.

[nensii21]

Rebased and addressed the review feedback. Removed the backend test split changes so this PR is focused only on Node.js runtime matrix coverage. Also consolidated the README runtime support documentation and updated the workflow to validate Node.js 20 and 22.

[nensii21]

Addressed the requested changes.

• Removed the backend test split changes so this PR no longer overlaps with ci: split backend unit and integration test suites #673.
• Kept the PR focused on Node.js runtime matrix coverage.
• Updated CI to validate Node.js 20 and 22.
• Consolidated the README runtime support documentation into a single section.

All checks are now passing, including the Node.js matrix jobs.

[utksh1]

Re-reviewed the latest push. The workflow YAML matrix indentation is still off and the README runtime-support section is inserted awkwardly under Prerequisites. Please fix YAML formatting, keep docs placement clean, preserve final newlines, and rerun CI.

[nensii21]

Thanks for catching that. I've cleaned up the workflow changes, and force-pushed the updated commit.

Could you please re-review the latest commit when you have a chance? Thanks.

[utksh1]

Re-reviewed the latest commit. This still needs changes before merge.

The README change inserts the Runtime Support section inside the Mermaid architecture diagram, between PM --> PARSER[parser.py] and the execution-engine edges. That breaks the diagram and moves ## Prerequisites into the code block context.

Please move the runtime-support note to a normal README section outside the Mermaid block, keep the workflow YAML indentation clean, and preserve the final newline in .github/workflows/ci.yml.