Remove EUR/USD support — XAU/USD-only codebase

EUR/USD never had a validated edge (2026-07-11/12 verdict: no config
passed validation on M5/M15/H1 at 1-pip cost; cost-to-volatility root
cause). Removed: EurUsdStrategyConfig, pair_signals/eurusd.py, EUR
gates 6h + weekend/day filters + strategy marker + trade geometry in
signal_aggregator, EUR pair registry/aliases in main.py and
gpu_backtest.py, EUR/USD news pair mappings, test_all.py Module 10.
Generic multi-currency news keyword infra kept (GBP/JPY/EUR keyword
table is not pair code). Full EUR history remains at 7d3fd95.

Suite: 162/162 green (was 187; 25 EUR-specific tests removed).

Claude-Session: https://claude.ai/code/session_015kby7M9JwpYi8NQT2yoxAi

main.py

@@ -21,7 +21,7 @@ if hasattr(sys.stdout, "reconfigure"):
 if hasattr(sys.stderr, "reconfigure"):
     sys.stderr.reconfigure(encoding="utf-8")
 
-from config import PlatformConfig, Timeframe, SignalStrength, XAUUSD, EURUSD
+from config import PlatformConfig, Timeframe, SignalStrength, XAUUSD
 from pair_signals import PAIR_PRODUCERS
 from signal_aggregator import SignalAggregator, SignalReport
 
@@ -99,7 +99,7 @@ def _compact_reason(reason: str) -> str:
 
 
 def _fmt_price(price: float) -> str:
-    """2dp for gold-scale prices, 5dp for FX-scale (EUR/USD etc.)."""
+    """2dp for gold-scale prices, 5dp for sub-10 FX-scale prices."""
     return f"{price:.2f}" if price >= 10 else f"{price:.5f}"
 
 
@@ -257,7 +257,7 @@ Examples:
         """,
     )
     parser.add_argument("--pair", "-p", default="XAUUSD",
-                        help="Pair to analyze: XAUUSD | EURUSD (default: XAUUSD)")
+                        help="Pair to analyze: XAUUSD (default: XAUUSD)")
     parser.add_argument("--timeframe", "-tf", default="H1",
                         choices=["M5", "M15", "M30", "H1", "H4", "D1"],
                         help="Primary analysis timeframe (default: H1)")
@@ -274,7 +274,6 @@ Examples:
 def _resolve_pair(s: str) -> str:
     aliases = {
         "XAUUSD": XAUUSD, "XAU/USD": XAUUSD, "GOLD": XAUUSD,
-        "EURUSD": EURUSD, "EUR/USD": EURUSD, "EUR": EURUSD,
     }
     key = s.upper().strip()
     if key in aliases: