fix(add-changeset): shorten frontmatter description for audit compliance

[unional]

Summary

• Shorten the add-changeset frontmatter description to ≤120 characters with required trigger phrasing
• Move example trigger phrases (add cs, missing changeset CI) into the skill body

These changes mirror improvements made in repobuddy/repobuddy to pass skill audit Q1 and Q5 checks.

Test plan

• Run npx cyber-skills@0.4.3 audit validate against the updated skill
• Confirm no files outside skills/add-changeset/ were modified

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Made with Cursor

[changeset-bot]

⚠️ No Changeset found

Latest commit: 05f6ec4

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.

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