Refocus on USD/JPY and add walk-forward backtester with regime filter

- Strip multi-pair plumbing; drop synthetic-data fallback
- Add BacktestConfig + walk-forward replay through the live signal pipeline
- Add metrics module (PF, Sharpe, Sortino, max DD, trade journal)
- Add parallel grid optimizer with disk parquet cache
- Add H4 ADX regime gate (--regime-filter, --regime-min-adx) — cuts chop
  losses ~84% in 2023 H1 while preserving trend edge

news_engine.py

@@ -413,15 +413,7 @@ class NewsEngine:
 
     @staticmethod
     def _get_affected_pairs(currency: str) -> List[str]:
-        """Get all major pairs affected by a currency event."""
-        pairs = {
-            "USD": ["EURUSD=X", "GBPUSD=X", "USDJPY=X", "USDCHF=X", "AUDUSD=X", "USDCAD=X", "NZDUSD=X"],
-            "EUR": ["EURUSD=X", "EURGBP=X", "EURJPY=X", "EURCHF=X"],
-            "GBP": ["GBPUSD=X", "EURGBP=X", "GBPJPY=X"],
-            "JPY": ["USDJPY=X", "EURJPY=X", "GBPJPY=X", "AUDJPY=X", "CADJPY=X"],
-            "CHF": ["USDCHF=X", "EURCHF=X"],
-            "AUD": ["AUDUSD=X", "AUDJPY=X"],
-            "CAD": ["USDCAD=X", "CADJPY=X"],
-            "NZD": ["NZDUSD=X"],
-        }
-        return pairs.get(currency, [])
+        """Map a currency event to USD/JPY (the only watched pair)."""
+        if currency in ("USD", "JPY"):
+            return ["USDJPY=X"]
+        return []