[Feature]: Add Fear and Greed Crypto Sentiment Index Tool (Python)

### Description Create a Python tool in `tools/crypto_fear_greed_index/` that fetches the daily Crypto Fear and Greed Index score and historical sentiment ratings (Extreme Fear, Fear, Neutral, Greed, Extreme Greed) from the public Alternative.me API. ### Acceptance Criteria - [ ] Directory `tools/crypto_fear_greed_index/` with `tool.py`, `metadata.json`, `requirements.txt`, and `README.md`. - [ ] Parameters: `days` (int, default 7, max 30). - [ ] Returns current sentiment score (0-100), classification label, and multi-day trend history. - [ ] Passes `python3 scripts/validate_tools.py`.