chore: add guardrails for PR's

[nhironaka]

Summary

Updating ./cursor/BUGBOT.md

Screenshots (if appropriate):

Testing approaches

---

Note

Low Risk
Documentation-only change to .cursor/BUGBOT.md; no runtime, API, or dependency impact.

Overview
Extends .cursor/BUGBOT.md with a PR readiness section so automated review checks the PR before diving into code.

Reviewers (and Bugbot) are told to flag oversized or mixed-concern diffs (e.g. ~400-line ideal, one component per PR, isolated token cascades), thin descriptions (what / why / how verified, including AI boilerplate), and changeset level vs. actual API impact, as top-level comments—not inline nits.

A new automated checks table maps CI signals (PR comment bot, story coverage, export/publint/attw, Storybook axe, Chromatic, package size) and says to flag when failures aren’t explained in the description. A horizontal rule separates this block from the existing “What to focus on” review priorities.

^{Reviewed by Cursor Bugbot for commit 90831b4. Bugbot is set up for automated code reviews on this repo. Configure here.}

[changeset-bot]

⚠️ No Changeset found

Latest commit: 90831b4

Merging this PR will not cause a version bump for any packages. If these changes should not result in a new version, you're good to go. If these changes should result in a version bump, you need to add a changeset.

This PR includes no changesets

When changesets are added to this PR, you'll see the packages that this PR includes changesets for and the associated semver types

Click here to learn what changesets are, and how to add one.

Click here if you're a maintainer who wants to add a changeset to this PR

[devin-ai-integration]

✅ Devin Review: No Issues Found

Devin Review analyzed this PR and found no bugs or issues to report.