Skill follow-up: process-skill-router

## Summary
Address the follow-up actions for the process-skill-router skill as identified in the skills review.

## Acceptance Criteria
- [ ] Add a small decision tree test matrix and sample prompts mapped to routes.

## Scope
- Applies to `skills/process-skill-router/`
- Derived from skills-review.md (commit 9c59dbc)

## Parent
- Refs: #297
