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Add two new OI-derived features to improve ML model's market microstructure understanding: - oi_change_ma5: 5-candle moving average of OI change rate (short-term trend) - oi_price_spread: z-scored OI minus z-scored price return (divergence signal) Both features use 96-candle rolling z-score window. FEATURE_COLS expanded from 24 to 26. Existing tests updated to reflect new feature counts. Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>