Skill follow-up: technical-debt-prioritisation

## Summary
Address the follow-up actions for the technical-debt-prioritisation skill as identified in the skills review.

## Acceptance Criteria
- [ ] Add a worked scoring example and a sample debt register.

## Scope
- Applies to `skills/technical-debt-prioritisation/`
- Derived from skills-review.md (commit 9c59dbc)

## Parent
- Refs: #297
