fix(add-changeset): trim token bloat (~20% reduction)

[unional]

Summary

• Remove redundant intro paragraph (restates the frontmatter description — already in agent context)
• Collapse verbose summary rules (7-bullet list + Good/Bad examples) into one dense line
• Remove ## What Happens Next section — describes CI pipeline behavior the agent cannot act on; belongs in project docs, not a skill body
• Keep breaking-change Migration: format noted inline in the condensed summary rule

Net: 168 → 134 lines (~20% fewer tokens loaded on every invocation).

Test plan

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

🤖 Generated with Claude Code

[changeset-bot]

⚠️ No Changeset found

Latest commit: 2a31090

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