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>

signal_aggregator.py

@@ -31,14 +31,10 @@ from news_engine import NewsEngine, FundamentalContext
 logger = logging.getLogger(__name__)
 
 
-# Per-symbol full TF list (primary + confirmations). Overrides the global
-# config.confirmation_timeframes for these symbols only — forex pairs are
-# unaffected. XAU/XAG use M15+H1+H4 (no D1 since yfinance daily for futures
-# is unreliable; H4 is resampled from H1 in data_provider).
-_PER_SYMBOL_TFS: Dict[str, List[Timeframe]] = {
-    "XAUUSD=X": [Timeframe.M15, Timeframe.H1, Timeframe.H4],
-    "XAGUSD=X": [Timeframe.M15, Timeframe.H1, Timeframe.H4],
-}
+# Per-symbol TF overrides. Currently empty — all forex pairs use the global
+# config.confirmation_timeframes. Add entries here only if a specific symbol
+# needs a different MTF set.
+_PER_SYMBOL_TFS: Dict[str, List[Timeframe]] = {}
 
 
 @dataclass