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>

telegram_bot.py

@@ -25,6 +25,14 @@ from datetime import datetime
 from typing import Dict, List, Optional, Tuple
 from zoneinfo import ZoneInfo
 
+# Load .env so TELEGRAM_BOT_TOKEN / GEMINI_API_KEY / TWELVE_DATA_API_KEY
+# don't need to be exported manually.
+try:
+    from dotenv import load_dotenv
+    load_dotenv()
+except ImportError:
+    pass
+
 from telegram import BotCommand, Update
 from telegram.constants import ParseMode
 from telegram.ext import Application, CommandHandler, ContextTypes
@@ -43,8 +51,8 @@ logger = logging.getLogger(__name__)
 SCAN_TIMEFRAMES = ["M15", "H1"]  # two cards (M15 and H1) per /scan; cache shared
 
 # Pairs analyzed by the /scan command. Limited to the most liquid majors
-# plus gold to keep credits low and signal quality high.
-SCAN_PAIRS = ["EURUSD=X", "USDJPY=X", "GBPUSD=X", "XAUUSD=X"]
+# to keep credits low and signal quality high.
+SCAN_PAIRS = ["EURUSD=X", "USDJPY=X", "GBPUSD=X", "AUDUSD=X"]
 
 _TF_MAP = {
     "M5":  Timeframe.M5,  "M15": Timeframe.M15,