Stop committing the shipmill plugin to .claude/settings.json (#112)

shipmill is each person's choice, not a requirement of the repo
(shipmill/shipmill#702): install it at user scope instead.

Co-authored-by: Romamo <github@romavm.dev>
Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>

Author: 3 people