Add direct provider-to-engine backtest harness

[luisleo526]

Summary

• add an ABI-checked Python backtest runner that copies full PineForge reports safely
• add pineforge-backtest and a repository script to fetch CCXT OHLCV and run a compiled strategy without CSV
• include provenance, trades, metrics, diagnostics, traces, and equity curve in JSON output
• document the Python/C++ provider bucket model and harness usage

Validation

• Ruff
• strict mypy
• 28 pytest tests
• wheel and sdist build
• live Kraken -> compiled MACD strategy smoke test (481 bars, 34 trades, 481 equity points)
• ctypes report layout checked against the C++ header (size 944, metrics offset 160)