Skill follow-up: requirements-gathering

## Summary
Address the follow-up actions for the requirements-gathering skill as identified in the skills review.

## Acceptance Criteria
- [ ] Add a concise question bank by work type and a validation checklist for ÔÇ£enough infoÔÇØ.

## Scope
- Applies to `skills/requirements-gathering/`
- Derived from skills-review.md (commit 9c59dbc)

## Parent
- Refs: #297
