Skill: Update ButterCut

Updates ButterCut to the latest version. Uses git pull if available, otherwise downloads from GitHub.

Before updating, always make a backup and encourage the user to save it to a location outside the ButterCut directory. Verify the most recent backup exists and offer to copy it to their Desktop or iCloud Drive.

Workflow

1. Check current version:

cat lib/buttercut/version.rb

2. Check if git repo:

git rev-parse --git-dir 2>/dev/null