Reduce verbosity in reviewing-changes skill for clean PRs

Problem: PR #6117 review produced ~800 tokens of excessive praise and
unnecessary sections when no issues were found. Expected output should
have been ~30 tokens: "APPROVE - Clean refactoring".

Changes:
- SKILL.md: Add "Clean PRs" section with explicit 2-3 line format
- SKILL.md: Make "minimal reviews" first core principle
- review-psychology.md: Elevate brevity guidance to first directive
- review-outputs.md: Add Example 7 showing PR #6117 as anti-pattern
- refactoring.md: Replace verbose example with clean vs issues examples
- Add IMPLEMENTATION_PLAN.md documenting rationale and approach

Expected Impact:
- 70-90% token reduction for clean PRs (800 → 30-100 tokens)
- Maintains comprehensive reviews for PRs with actual issues
- Reduces noise in PR conversations
- Faster approvals for good work

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <[email protected]>

Author: SaintPatrck