Add pair_signals per-pair producer registry

Ported from feature/eurusd-support: PAIR_PRODUCERS registry with
make_config() factories per pair. xauusd.make_config is a pure
PlatformConfig-defaults wrapper (equality with the inline construction
is enforced by test); eurusd.make_config carries the donor branch's
regime weights and gates as a pre-realism baseline.

Adds 4 registry tests. 154/154 pass.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

pair_signals/xauusd.py

@@ -0,0 +1,29 @@
+"""XAU/USD signal producer config.
+
+PlatformConfig defaults ARE the tuned XAU/USD configuration, so this
+factory only sets the timeframes. It must stay equivalent to the inline
+PlatformConfig(symbol=XAUUSD, ...) construction used by the backtester
+and Telegram bot (enforced by a test in test_all.py).
+"""
+
+from typing import Optional, List
+from config import PlatformConfig, Timeframe
+
+_CONFIRMATIONS = {
+    Timeframe.M5:  [Timeframe.M15, Timeframe.H1],
+    Timeframe.M15: [Timeframe.M5, Timeframe.H1],
+    Timeframe.H1:  [Timeframe.M15, Timeframe.H4],
+    Timeframe.H4:  [Timeframe.H1, Timeframe.D1],
+}
+
+
+def make_config(
+    primary_tf: Timeframe,
+    confirmation_tfs: Optional[List[Timeframe]] = None,
+) -> PlatformConfig:
+    config = PlatformConfig()
+    config.primary_timeframe = primary_tf
+    config.confirmation_timeframes = (
+        confirmation_tfs or _CONFIRMATIONS.get(primary_tf, [Timeframe.M15, Timeframe.H4])
+    )
+    return config