ci: stage npm releases before publishing

[JoviDeCroock]

Summary

• Switch the release workflow from direct changeset publish to staging the package with npm stage publish.
• Add a small staging helper that skips already-published versions, derives the dist-tag from the package version, stages with the configured public access, and surfaces stage IDs when npm returns them.
• Bump the workflow npm install to npm@^11.15.0, which is required for staged publishing.

Why

This keeps CI responsible for preparing the release artifact, but moves the final public publish behind maintainer approval with 2FA via npm stage approve <stage-id> or npmjs.com.