Add real price extraction for overlay replay

[Pigbibi]

Summary

• add a dependency-free price-history adapter that accepts both date and as_of CSV schemas
• add an extraction CLI for compact replay inputs from existing QuantStrategyLab price files
• document real-price replay workflow and cover it in CI/tests

Validation

• python -m pytest -q
• python scripts/validate_latest_signal.py examples/latest_signal.example.json
• python scripts/extract_price_history.py --source examples/price_history.example.csv --target /tmp/qqq_overlay_prices.csv --symbols QQQ
• python scripts/backtest_signal_overlay.py --prices /tmp/qqq_overlay_prices.csv --signals examples/signal_history --symbol QQQ --output /tmp/qqq_overlay_summary.json
• slowrun bash -lc "python scripts/extract_price_history.py --source ../UsEquitySnapshotPipelines/data/output/tqqq_growth_income_real_full_archive_2026-05-26/price_history.csv --target /tmp/real_qqq_price_history.csv --symbols QQQ --start-date 2025-01-01 && python scripts/backtest_signal_overlay.py --prices /tmp/real_qqq_price_history.csv --signals examples/signal_history --symbol QQQ --output /tmp/real_qqq_overlay_summary.json"