feat(sidebar): add sub-article navigation

[omribz156]

Summary:

• Add sidebar entries for nested Diagnostics and Node-API child articles.
• Keep parent topic pages reachable through Overview links inside each nested group.

Verification:

• npm run format:check -- site.json
• npm run lint
• npm run build
• Targeted Node script verified every added nested sidebar link exists under pages/.

This was implemented with Codex assistance, with the final diff reviewed before posting.

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Project	Deployment	Actions	Updated (UTC)
nodejs-learn	Ready	Preview	May 16, 2026 10:11am

[github-actions]

👋 Codeowner Review Request

The following codeowners have been identified for the changed files:

Team reviewers: @nodejs/nodejs-website

Please review the changes when you have a chance. Thank you! 🙏

[cursor]

PR Summary

Low Risk
Low risk, data-only navigation changes confined to site.json; main risk is broken/incorrect links or unintended sidebar nesting/ordering.

Overview
Adds nested sidebar navigation under Learn for several Diagnostics topics (Memory, Live Debugging, Poor Performance) and Node-API sections (Getting Started, Build Tools, Special Topics).

Each newly-nested section now includes an explicit Overview child entry so the parent landing page remains directly reachable from the expanded group.

^{Reviewed by Cursor Bugbot for commit 663332c. Bugbot is set up for automated code reviews on this repo. Configure here.}

[avivkeller]

I think this link can be removed, right?