feat(backtest): add rolling walk-forward validation and Monte Carlo trade permutation test

- monte_carlo_trade_pvalue(): shuffles trade P&L N times, returns fraction of
  permuted sequences that beat real total return (p<0.05 = genuine edge)
- walk_forward_rolling(): multiple IS/OOS windows (IS=3yr, OOS=1yr, step=1yr),
  computes wf_oos_sharpe_mean, wf_oos_consistency (% profitable windows)
- backtest_signal_ftmo(): new wf_rolling and mc_n_permutations params
- Strategy generator: enables both (200 MC permutations), adds mc_ok and wf_ok
  to acceptance filter (mc_p<0.20, wf_consistency>=50%)
- Rebacktest script: enables both, stores all wf_*/mc_* fields in write-back
- 6 new tests covering MC pvalue, disabled-by-default, zero-trades edge case,
  rolling WF key presence and consistency range

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

rdagent/components/backtesting/__init__.py

@@ -11,16 +11,23 @@ from .vbt_backtest import (
     FTMO_MAX_LEVERAGE,
     FTMO_RISK_PER_TRADE,
     OOS_START_DEFAULT,
+    WF_IS_YEARS,
+    WF_OOS_YEARS,
+    WF_STEP_YEARS,
     backtest_from_forward_returns,
     backtest_signal,
     backtest_signal_ftmo,
+    monte_carlo_trade_pvalue,
+    walk_forward_rolling,
 )
 
 __all__ = [
     'BacktestMetrics', 'FactorBacktester', 'ResultsDatabase',
     'CorrelationAnalyzer', 'PortfolioOptimizer', 'AdvancedRiskManager',
     'backtest_signal', 'backtest_signal_ftmo', 'backtest_from_forward_returns',
+    'monte_carlo_trade_pvalue', 'walk_forward_rolling',
     'DEFAULT_BARS_PER_YEAR', 'DEFAULT_TXN_COST_BPS',
     'FTMO_INITIAL_CAPITAL', 'FTMO_MAX_DAILY_LOSS', 'FTMO_MAX_TOTAL_LOSS',
     'FTMO_MAX_LEVERAGE', 'FTMO_RISK_PER_TRADE', 'OOS_START_DEFAULT',
+    'WF_IS_YEARS', 'WF_OOS_YEARS', 'WF_STEP_YEARS',
 ]