Update Node.js LTS to v20.20.1

[PeterDaveHello]

Description

Node.js v20 entered Maintenance LTS six months ago. Update the version from v20.19.0 (released over a year ago) to v20.20.1, the latest LTS release this month.

This ensures the project leverages recent Node.js improvements, including security updates, and stays on a supported LTS track.

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Checklist

• I've read the contributing guide
• [] The relevant docs, if any, have been updated or created
• [] The relevant tests, if any, have been updated or created

Tests

No tests updated, passed CI should be good enough.

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Summary by cubic

Update Node.js LTS to v20.20.1 across the repo to pick up security fixes and keep a consistent runtime. Updated .nvmrc, .node-version, engine constraints, installer scripts, and docs; the @continuedev/cli installers now require 20.20.1.

• Migration
  • Upgrade Node to 20.20.1 (run nvm use or install from nodejs.org).
  • Reinstall dependencies to rebuild any native modules.
  • Update CI to use Node 20.20.1 if pinned.

^{Written for commit f0bdadb. Summary will update on new commits.}

[github-actions]

All contributors have signed the CLA ✍️ ✅
_{Posted by the CLA Assistant Lite bot.}

[PeterDaveHello]

I have read the CLA Document and I hereby sign the CLA

[cubic-dev-ai]

No issues found across 16 files