Quant: Walk-forward eval framework

Walk-forward IC measurement + portfolio backtest harness.

Files: Omni/Fund/Quant/Eval.hs, Omni/Fund/Quant/Test.hs

Deliverables:

Eval types:

• SignalEval — IC, IC std, ICIR, hit rate, t-stat, decay curve
• PortfolioEval — total return, annualized, Sharpe, max drawdown, Calmar
• EvalConfig — universe, train/test split, rebalance freq, horizons, min thresholds

Core functions:

• spearmanCorrelation :: [Double] -> [Double] -> Double
• evalSignalIC :: EvalConfig -> SignalFn -> Map Text [DailyBar] -> SignalEval
• signalPasses :: EvalConfig -> SignalEval -> Bool
• evalPortfolio :: EvalConfig -> SignalFn -> Map Text [DailyBar] -> (PortfolioEval, PortfolioEval) — strategy vs equal-weight
• maxDrawdown :: [Double] -> Double
• runEvalSuite :: EvalConfig -> IO () — full eval runner with pass/fail output

Default config: Train 2020-2023, test 2024-2025, weekly rebalance, IC > 0.02, t > 2.0.

Test.hs: Property tests for Spearman correlation, golden tests for momentum IC on synthetic data, integration test loading cached market data and running full eval.

This is the gate — if eval doesn't pass, nothing proceeds to Phase 2.