Add comprehensive project documentation and fix data pipeline

- Add detailed README with architecture diagram and usage instructions
- Add API, configuration, and development documentation
- Fix price data column handling for yfinance auto_adjust=True
- Fix model feature dimension indexing and temporal attention batching
- Add missing imports and position tracking in paper broker
- Add python-dotenv support for environment variables
- Update .gitignore with Python artifacts and environment files

.gitignore

@@ -1 +1,7 @@
 implementation.md
+.env
+*.log
+__pycache__/
+*.py[cod]
+*.pkl
+*.db