H-6373: Change publishing lifecycle scripts; add changeset for @hashintel/refractive

[CiaranMn]

🌟 What is the purpose of this PR?

Fixes to published packages / publishing process:

1. Switch the lifecycle script for pre-publishing build to prepublishOnly consistently: a few packages had prepare, and somehow @hashintel/ds-helpers ended up being published without its built styled-system folder. I'm not sure this will fix it but it's worth a try.
2. Add a changeset for @hashintel/refractive to get a new version published – the export names were changed but the published version still has the old exports, meaning using @hashintel/petrinaut in other repos fails (because it refers to the new, unpublished function names).
3. Adds a README for ds-helpers

[vercel]

The latest updates on your projects. Learn more about Vercel for GitHub.

Project	Deployment	Actions	Updated (UTC)
hash	Ready	Preview, Comment	Mar 25, 2026 5:57pm
hashdotdesign	Ready	Preview, Comment	Mar 25, 2026 5:57pm
hashdotdesign-tokens	Ready	Preview, Comment	Mar 25, 2026 5:57pm
petrinaut	Ready	Preview, Comment	Mar 25, 2026 5:57pm

[cursor]

PR Summary

Low Risk
Low risk because changes are limited to npm lifecycle scripts, a small README addition, and patch changesets; the main risk is altered publish/build timing that could affect release automation.

Overview
Ensures design-system packages build at publish time by replacing the prepare script with prepublishOnly in @hashintel/ds-components, @hashintel/ds-helpers, and @hashintel/ds-theme.

Adds patch changesets to release @hashintel/refractive (to publish equation export casing changes) and @hashintel/ds-helpers (to address publishing output issues), and introduces a new README.md for @hashintel/ds-helpers.

^{Written by Cursor Bugbot for commit 1bb25c8. This will update automatically on new commits. Configure here.}