Add yfinance fallback for gold/silver + coarse Telegram progress

- yfinance>=0.2.40 added as a hard dependency
- _fetch_yfinance_fallback(): pulls OHLCV from Yahoo for symbols not on
  the Twelve Data free tier (XAUUSD → GC=F, XAGUSD → SI=F)
- Hooked into both batch and single-symbol fetch paths; logs as [yf]
  to distinguish from Twelve Data [live]
- Fail-loud: if both providers return nothing, the pair is skipped with
  the existing "data unavailable" message
- _analyze_all_tfs accepts an async progress callback; both /signal and
  /scan now show coarse milestones via message edits:
    "📡 Fetching market data..."  →  "🧠 Analyzing pairs..."  →  result
- prefetch_batch is now run in a thread so it doesn't block the event loop

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

data_provider.py

@@ -17,11 +17,35 @@ from typing import Dict, List, Optional
 import pandas as pd
 import requests
 
+try:
+    import yfinance as yf
+    _YF_AVAILABLE = True
+except ImportError:
+    yf = None
+    _YF_AVAILABLE = False
+
 from config import PlatformConfig, Timeframe, SYMBOL_DISPLAY, PIP_VALUES
 
 logger = logging.getLogger(__name__)
 _no_data_warned: set = set()  # suppress duplicate "no data" warnings per symbol
 
+# Symbols that Twelve Data free tier does not support — route to Yahoo Finance.
+# Gold/silver futures are the most reliable Yahoo symbols (full OHLCV history).
+_YF_FALLBACK_MAP = {
+    "XAUUSD=X": "GC=F",
+    "XAGUSD=X": "SI=F",
+}
+
+_YF_INTERVALS = {
+    Timeframe.M1:  "1m",
+    Timeframe.M5:  "5m",
+    Timeframe.M15: "15m",
+    Timeframe.M30: "30m",
+    Timeframe.H1:  "1h",
+    Timeframe.D1:  "1d",
+    Timeframe.W1:  "1wk",
+}
+
 
 class DataIntegrityError(Exception):
     """Raised when data fails validation checks."""
@@ -227,6 +251,57 @@ class ForexDataProvider:
 
     # ── Private Methods ────────────────────────────────────────────
 
+    def _fetch_yfinance_fallback(
+        self, symbol: str, timeframe: Timeframe
+    ) -> Optional[pd.DataFrame]:
+        """
+        Fetch OHLCV from Yahoo Finance for symbols Twelve Data doesn't cover
+        on the free tier (XAUUSD, XAGUSD). Returns None if not mapped or fails.
+        """
+        if not _YF_AVAILABLE:
+            return None
+        yf_symbol = _YF_FALLBACK_MAP.get(symbol)
+        yf_interval = _YF_INTERVALS.get(timeframe)
+        if yf_symbol is None or yf_interval is None:
+            return None
+
+        # Yahoo intraday limits: 1m → last 7d, 15m/30m/1h → last 60d
+        if yf_interval in ("1m", "2m"):
+            period = "7d"
+        elif yf_interval in ("5m", "15m", "30m", "60m", "1h"):
+            period = "60d"
+        else:
+            period = "2y"
+
+        try:
+            df = yf.download(
+                yf_symbol, interval=yf_interval, period=period,
+                progress=False, auto_adjust=False, threads=False,
+            )
+            if df is None or df.empty:
+                return None
+
+            # Single-symbol download can return MultiIndex columns in newer yfinance versions
+            if isinstance(df.columns, pd.MultiIndex):
+                df.columns = df.columns.get_level_values(0)
+
+            # Normalise to UTC tz-aware index
+            if df.index.tz is None:
+                df.index = df.index.tz_localize("UTC")
+            else:
+                df.index = df.index.tz_convert("UTC")
+            df.index.name = "Datetime"
+
+            df = df[["Open", "High", "Low", "Close", "Volume"]].copy()
+            logger.info(
+                f"[yf] {yf_symbol} {yf_interval}: {len(df)} bars, "
+                f"last close={df['Close'].iloc[-1]:.5f}"
+            )
+            return df
+        except Exception as e:
+            logger.warning(f"yfinance fallback failed for {symbol} {timeframe.value}: {e}")
+            return None
+
     def _throttle(self, credits: int = 1) -> None:
         """
         Block until `credits` per-minute API credits are available.
@@ -343,6 +418,14 @@ class ForexDataProvider:
 
                 values = sym_data.get("values")
                 if not values:
+                    # Try yfinance fallback for unsupported symbols (XAU, XAG)
+                    yf_df = self._fetch_yfinance_fallback(symbol, timeframe)
+                    if yf_df is not None:
+                        yf_df = self._validate_and_clean(yf_df, symbol, timeframe)
+                        cache_key = f"{symbol}_{timeframe.value}"
+                        self._cache[cache_key] = yf_df
+                        self._cache_timestamps[cache_key] = now
+                        continue
                     if td_sym not in _no_data_warned:
                         logger.warning(f"No data from Twelve Data for {td_sym} — symbol may require a paid plan.")
                         _no_data_warned.add(td_sym)
@@ -378,8 +461,13 @@ class ForexDataProvider:
         """
         Fetch OHLCV from Twelve Data REST API.
         Raises DataUnavailableError when data cannot be retrieved.
+        Falls back to yfinance for symbols not on the Twelve Data free tier.
         """
         if not self._api_key:
+            # No Twelve Data key — try yfinance fallback for mapped symbols
+            yf_df = self._fetch_yfinance_fallback(symbol, timeframe)
+            if yf_df is not None:
+                return yf_df
             raise DataUnavailableError(
                 "No Twelve Data API key — set the TWELVE_DATA_API_KEY environment variable."
             )
@@ -417,6 +505,9 @@ class ForexDataProvider:
 
             values = data.get("values")
             if not values:
+                yf_df = self._fetch_yfinance_fallback(symbol, timeframe)
+                if yf_df is not None:
+                    return yf_df
                 raise DataUnavailableError(
                     f"No data returned for {td_symbol} — symbol may require a paid plan."
                 )