Tighten signal pipeline: yfinance-only XAU/XAG, leaner Telegram /scan

- XAU/XAG always route to Yahoo Finance and skip Twelve Data entirely
  (excluded from batch prefetch, served per-symbol via yfinance).
- Daily chart cleanly skipped for gold/silver — engine drops it from MTF.
- Telegram /scan limited to EURUSD, USDJPY, GBPUSD, XAUUSD.
- SCAN_TIMEFRAMES reduced to single H1 primary; engine still pulls
  M15+H1+D1 internally via confirmation TFs (halves API credits per scan).
- Default confirmation TFs swapped H4 -> D1 in config and main.py.
- mtf_agreement_threshold kept at 2-of-3.
- CLAUDE.md cleaned up — old XAUUSD/synthetic-data bug reports removed.

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

config.py

@@ -187,7 +187,7 @@ class PlatformConfig:
     # Analysis timeframes (primary + confirmation)
     primary_timeframe: Timeframe = Timeframe.H1
     confirmation_timeframes: List[Timeframe] = field(
-        default_factory=lambda: [Timeframe.M15, Timeframe.H4]
+        default_factory=lambda: [Timeframe.M15, Timeframe.D1]
     )
 
     # Data source