02e0b0ccab
Three bugs fixed:
1. **Weighted average entry price for risk management**:
- Previously, entry_price was overwritten on each buy, causing stop loss
to be calculated from the latest buy price instead of average
- Added cost_basis tracking and average_entry_price property
- Stop loss now correctly uses weighted average across all buys
2. **Portfolio value accumulation in _calculate_metrics**:
- Bug: running_position = trade['quantity'] was OVERWRITING position
- Fix: running_position += trade['quantity'] to properly accumulate DCA
3. **Risk management exit reset**:
- Added cost_basis reset when position is closed
Max drawdown is now correctly bounded by stop loss percentage (~5%)
instead of showing inflated values like 59%.