Engineering setup compatibility entry point

Engineering setup now lives in /setup.

Locate the installed setup skill through the available-skills list or a sibling skill folder. Read its SKILL.md and follow it to configure engineering workflows for the target project. Its references resolve relative to the setup skill directory.

If setup is unavailable, tell the user to install it with npx skills add jny986/ai-setup --skill setup for their agent, then run /setup. Report the missing dependency instead of claiming setup is complete.