Skill follow-up: quality-gate-enforcement

## Summary
Address the follow-up actions for the quality-gate-enforcement skill as identified in the skills review.

## Acceptance Criteria
- [ ] Add sample gate configs for common stacks and a baseline coverage ratchet example.

## Scope
- Applies to `skills/quality-gate-enforcement/`
- Derived from skills-review.md (commit 9c59dbc)

## Parent
- Refs: #297
