engine-setup-external-contributionlisted

<!-- GENERATED by .engine/tools/codex_gen.py from .claude/skills/engine-setup-external-contribution/SKILL.md — edit that source and regenerate; never edit this file by hand. --> ## Steps 1. Check whether the `external-contribution` add-on is installed in this project. 2. If it is not installed, explain in plain language what it does and offer to add it through the normal setup step — never install it because this route matched; adding it is the operator's decision. 3. If it is installed, report the active capability and route the operator's request to the add-on's own workflow.