Skill follow-up: skills-first-workflow

## Summary
Address the follow-up actions for the skills-first-workflow skill as identified in the skills review.

## Acceptance Criteria
- [ ] Add a validation script or sample commands to prove each prerequisite.

## Scope
- Applies to `skills/skills-first-workflow/`
- Derived from skills-review.md (commit 9c59dbc)

## Parent
- Refs: #297
