gh aw upgrade creates Copilot agent files in repos that don't use the Copilot engine #68872

gh aw init only creates .github/agents/agentic-workflows.md and .github/workflows/copilot-setup-steps.yml with --engine copilot, and it can skip them with --no-agent, --no-mcp and --no-skill. gh aw upgrade always writes them, along with .github/skills/agentic-workflows/SKILL.md, and has no matching flags.

Repro (gh-aw v0.91.12): in a repo whose only workflow sets engine: claude, run gh aw upgrade --no-fix or gh aw upgrade --no-fix --engine claude. Both create all three paths.

Expected: upgrade applies the same rules as init: it writes the Copilot agent and setup-steps workflow only when a workflow uses the Copilot engine (or when they already exist), and it accepts --no-agent, --no-mcp and --no-skill.

Impact: each upgrade adds files the repo doesn't use. They have to be deleted by hand, and in our case the generated copilot-setup-steps.yml also fails the repo's formatter check.