Always download the appropriate artifact

[desrosj]

This PR aims to prevent a failure when npm install is run when either the directory already exists or the the gutenberg/.gutenberg-hash file is missing (which means the script cannot currently confirm the correct version of the Gutenberg plugin is present).

• The postinstall command is changed from gutenberg:download to gutenberg:verify.
• The --force option has been removed. gutenberg:download will now download a fresh copy every time it's run.
• The gutenberg:verify script is now the preferred entry point for managing the files within the gutenberg directory. It will only trigger a downoad if the hashes do not match, or the folder is missing entirely.

Trac ticket: Core-64393.

Use of AI Tools

Claude was used to create the initial draft for this PR.

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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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[github-actions]

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Props desrosj.

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[ockham]

LGTM, and behaves as advertised in my local testing!

Disclaimer: I'm not super-familiar with the "new" build system and GB code sync, but AFAICS, the changes make sense to me.