feat(trading-scripts): add historical market data fetcher script
- Quick start, examples, outputs - AI integration guide - Cron setup, troubleshooting
- 1Y+ periods with auto-interval adjustment - Futures MultiIndex flattening + NaN dropna - Stats: total/annual returns, volatility, drawdown - Exports: Parquet/CSV/JSON + PNG/HTML charts - CLI groups for stocks/futures/crypto/meme