Remove yfinance/XAU/XAG fallback — focus on currency pairs only

- data_provider: strip yfinance imports, _YF_FALLBACK_MAP, _YF_INTERVALS,
  _YF_SESSION, _fetch_yfinance_fallback, _resample_h1_to_h4. Twelve Data
  is the sole data source. Raises DataUnavailableError if a pair isn't
  on the configured plan.
- config: remove XAU/USD and XAG/USD from SYMBOL_DISPLAY and PIP_VALUES.
  PIP_VALUES is now empty (defaults: 0.01 JPY pairs, 0.0001 forex).
- signal_aggregator: clear _PER_SYMBOL_TFS overrides (was XAU/XAG-only).
- telegram_bot: replace XAUUSD with AUDUSD in SCAN_PAIRS. Auto-load .env
  via python-dotenv so TELEGRAM_BOT_TOKEN/GEMINI_API_KEY are picked up.
- requirements: drop yfinance and curl_cffi dependencies.

End-to-end pipeline test passes: data freshness, news engine (Gemini live),
signal aggregator, and the /signal+/scan code paths in telegram_bot.

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

config.py

@@ -57,16 +57,12 @@ SYMBOL_DISPLAY = {
     "EURJPY=X": "EUR/JPY", "GBPJPY=X": "GBP/JPY",
     "AUDJPY=X": "AUD/JPY", "EURCHF=X": "EUR/CHF",
     "CADJPY=X": "CAD/JPY",
-    # Commodities
-    "XAUUSD=X": "XAU/USD", "XAGUSD=X": "XAG/USD",
 }
 
 # Pip values per symbol (used for trade setup risk/reward in pips)
-# Commodities and JPY pairs differ from the standard 0.0001 forex pip
-PIP_VALUES = {
-    "XAUUSD=X": 0.01,   # Gold: 1 pip = $0.01
-    "XAGUSD=X": 0.001,  # Silver: 1 pip = $0.001
-}
+# Forex defaults: 0.01 for JPY pairs, 0.0001 for everything else.
+# Override here for any pair that doesn't follow that rule.
+PIP_VALUES: Dict[str, float] = {}
 
 
 @dataclass