Build/Test Tools: Upgrade npm to v12

[manzoorwanijk]

Upgrades npm to v12 for Core and the bundled themes with a build process, mirroring WordPress/gutenberg#82732. npm v12 makes dependency install scripts, git dependencies and remote URL dependencies opt-in.

• devEngines and engines require npm >=12.0.2 in Core, Twenty Twenty-One, Twenty Twenty-Two and Twenty Twenty-Five.
• allowScripts denies every dependency install script, and strict-allow-scripts fails the install on unreviewed ones.
• allow-file = none extends the npm v12 git and remote URL restrictions to local tarballs.
• No script needs approval since Build/Test Tools: Replace grunt-contrib-imagemin with maintained optimizers #13562 replaced grunt-contrib-imagemin.

Trac ticket:

Use of AI Tools

AI assistance: Yes
Tool(s): Claude Code
Model(s): Claude Opus 5
Used for: Implementation and this description, reviewed by me.

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[github-actions]

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