XAU/XAG: 3-TF analysis (M15+H1+H4 resampled) via per-symbol override

- New _PER_SYMBOL_TFS map in signal_aggregator routes gold/silver to
  M15+H1+H4 confirmation; forex pairs untouched.
- H4 for XAU/XAG is resampled from yfinance H1 bars (yfinance has no
  native 4h candle). New _resample_h1_to_h4 helper.
- Batch prefetch unions per-symbol TFs so future per-pair overrides
  work without extra plumbing. XAU/XAG still excluded from Twelve Data
  batch — H4 resample triggers a single yfinance H1 fetch.
- Telegram SCAN_TIMEFRAMES restored to [M15, H1] so /scan emits both
  M15-primary and H1-primary cards. Shared cache means no extra credits.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

data_provider.py

@@ -169,13 +169,24 @@ class ForexDataProvider:
                 return cached
 
         # Symbols not on Twelve Data (gold, silver) always use yfinance.
-        # D1 is intentionally skipped for these — yfinance daily for futures
-        # is unreliable and the engine drops missing confirmation TFs cleanly.
+        # D1 is skipped (yfinance daily for futures is unreliable).
+        # H4 is resampled from H1 since yfinance has no native 4h candle.
         if symbol in _YF_FALLBACK_MAP:
             if timeframe == Timeframe.D1:
                 raise DataUnavailableError(
-                    f"Daily chart skipped for {symbol} — gold/silver use M15/H1 only."
+                    f"Daily chart skipped for {symbol} — gold/silver use M15/H1/H4 only."
                 )
+            if timeframe == Timeframe.H4:
+                h1_df = self._fetch_yfinance_fallback(symbol, Timeframe.H1)
+                if h1_df is None:
+                    raise DataUnavailableError(
+                        f"Yahoo Finance unavailable for {symbol} (H4 resample source H1)."
+                    )
+                df = self._resample_h1_to_h4(h1_df)
+                df = self._validate_and_clean(df, symbol, timeframe)
+                self._cache[cache_key] = df
+                self._cache_timestamps[cache_key] = now
+                return df
             yf_df = self._fetch_yfinance_fallback(symbol, timeframe)
             if yf_df is None:
                 raise DataUnavailableError(
@@ -277,6 +288,17 @@ class ForexDataProvider:
         }
         return fallback_spreads.get(symbol, 0.00020)
 
+    @staticmethod
+    def _resample_h1_to_h4(h1_df: pd.DataFrame) -> pd.DataFrame:
+        """Resample 1-hour OHLCV to 4-hour bars (yfinance has no native 4h)."""
+        return h1_df.resample("4h", label="right", closed="right").agg({
+            "Open":   "first",
+            "High":   "max",
+            "Low":    "min",
+            "Close":  "last",
+            "Volume": "sum",
+        }).dropna()
+
     def get_pair_info(self, symbol: str) -> Dict:
         """Return display name and pip value for a pair."""
         display = SYMBOL_DISPLAY.get(symbol, symbol)