[sirreal]

Upgrades the 6.1 branch to Node.js 24.x and npm 11.x. Also:

• Runs Grunt with --no-maglev --no-concurrent-sparkplug, as r63771 does on trunk, to avoid hangs at exit on Node.js 24.
• Regenerates package-lock.json with npm 11, whose npm ci rewrites the npm 6 lockfile, and sets legacy-peer-deps = true in .npmrc so npm 11 resolves peer dependencies as npm 6 did. No package versions change.
• Removes engine-strict = true from .npmrc. With it, npm 11 refuses to install the lint dependencies eslint-plugin-jsdoc 39.9.1 and @es-joy/jsdoccomment 0.36.1, whose engines exclude Node.js 24.

Trac ticket: TBD

Use of AI Tools

AI assistance: Yes
Tool(s): Claude Code
Model(s): Claude Opus 5.5
Used for: Applying the changes to each branch, regenerating the lockfile, building on Node.js 24 and comparing the output with the release, and drafting this description.

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This Pull Request is for code review only. Please keep all other discussion in the Trac ticket. Do not merge this Pull Request. See GitHub Pull Requests for Code Review in the Core Handbook for more details.

[github-actions]

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