fix(skill): rewrite risk-management-specialist with ISO 14971 content (#85)

- Rewrite SKILL.md from 226 to 538 lines with 12 triggers and TOC
- Add 5 numbered workflows with validation checkpoints
- Create references/iso14971-implementation-guide.md (~468 lines)
- Create references/risk-analysis-methods.md (~415 lines)
- Create scripts/risk_matrix_calculator.py (~419 lines)
- Delete 3 placeholder files (example_asset.txt, api_reference.md, example.py)
- Remove marketing language, use imperative voice throughout

Co-Authored-By: Claude Opus 4.5 <[email protected]>

Author: alirezarezvani