fix(trader): guard against division by zero and fix peak PnL logic

[chulinhcql-art]

This PR fixes a critical logic error in drawdown monitoring. It adds a safety check for zero entry prices and fixes the Peak PnL logic to correctly handle short positions. Authored by chulinhcql-art.

[chulinhcql-art]

Please use this Base (USDC) wallet for the reward: 0x061E613F450AefC5Ca0dB1A7764AE0545c968811. Thank you!

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[chulinhcql-art]

Critical fix for potential crash (division by zero). Highly recommend merging this to protect system stability.