docs: Add retrospective for skills improvement plan

[mcj-coder]

Overview

Create a retrospective document for the completed Skills Repository Improvement Plan (Phases 1-4).

Plan

Document the improvement plan outcomes including phase summaries, metrics, lessons learned, and recommendations.

Scope

Document:

• Phase summaries and deliverables
• What went well
• What could be improved
• Metrics and coverage improvements
• Recommendations for future work

Acceptance Criteria

• Retrospective created at docs/retrospectives/2026-01-16-skills-repository-improvement-plan.md (PR #387)
• PR created (PR #387)

References

• Phase 1 PR: docs: add skill format specification and references indexes #380
• Phase 2 PR: docs: consolidate skills with decision matrices and hierarchy #382
• Phase 3 PR: docs(skills): add Overview and Red Flags sections (Phase 3) #384
• Phase 4 Issue: docs: Phase 4 - Quality & Testing #385

[mcj-coder]

Plan

Create retrospective for the Skills Repository Improvement Plan covering:

1. Phase summaries with PR links
2. What went well analysis
3. What could be improved with lessons learned
4. Metrics and coverage improvements
5. Recommendations for future work

File location: docs/retrospectives/2026-01-16-skills-repository-improvement-plan.md