Replace Yahoo Finance with Polygon.io for chart data

- Add Polygon.io API client for reliable historical data access
- Update bot to use Polygon instead of Yahoo Finance for charts
- Add POLYGON_API_KEY to config and environment example
- Polygon free tier: 5 API calls/minute, more reliable than Yahoo
- Fallback to FinViz chart URL when Polygon unavailable

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

polygon_api.py

@@ -0,0 +1,115 @@
+"""Polygon.io API client for historical stock data."""
+import requests
+import logging
+from typing import Optional, Dict, List
+from datetime import datetime, timedelta
+
+logger = logging.getLogger(__name__)
+
+
+class PolygonAPI:
+    """Polygon.io implementation for historical stock data."""
+
+    def __init__(self, api_key: str):
+        """
+        Initialize Polygon API client.
+
+        Args:
+            api_key: Polygon.io API key
+        """
+        self.api_key = api_key
+        self.base_url = "https://api.polygon.io"
+
+    def get_candles(self, ticker: str, days: int = 30, resolution: str = 'D') -> Optional[Dict[str, List]]:
+        """
+        Retrieve historical candlestick data from Polygon.io.
+
+        Args:
+            ticker: Stock ticker symbol
+            days: Number of days of historical data to fetch
+            resolution: Candle resolution (ignored, always daily)
+
+        Returns:
+            Dictionary with OHLCV data or None if unavailable
+        """
+        try:
+            # Calculate date range
+            end_date = datetime.now()
+            start_date = end_date - timedelta(days=days)
+
+            # Format dates as YYYY-MM-DD
+            from_date = start_date.strftime('%Y-%m-%d')
+            to_date = end_date.strftime('%Y-%m-%d')
+
+            # Build API URL
+            url = f"{self.base_url}/v2/aggs/ticker/{ticker}/range/1/day/{from_date}/{to_date}"
+
+            # Make request
+            params = {
+                'adjusted': 'true',
+                'sort': 'asc',
+                'apiKey': self.api_key
+            }
+
+            logger.info(f"Fetching Polygon data for {ticker} from {from_date} to {to_date}")
+            response = requests.get(url, params=params, timeout=10)
+            response.raise_for_status()
+
+            data = response.json()
+
+            # Check if we got results
+            if data.get('status') != 'OK' or not data.get('results'):
+                logger.warning(f"No candle data available for ticker: {ticker}")
+                return None
+
+            results = data['results']
+
+            # Convert to expected format
+            timestamps = []
+            opens = []
+            highs = []
+            lows = []
+            closes = []
+            volumes = []
+
+            for candle in results:
+                # Polygon returns timestamp in milliseconds
+                timestamps.append(int(candle['t'] / 1000))
+                opens.append(float(candle['o']))
+                highs.append(float(candle['h']))
+                lows.append(float(candle['l']))
+                closes.append(float(candle['c']))
+                volumes.append(int(candle['v']))
+
+            logger.info(f"Successfully fetched {len(timestamps)} candles for {ticker}")
+
+            return {
+                'timestamps': timestamps,
+                'open': opens,
+                'high': highs,
+                'low': lows,
+                'close': closes,
+                'volume': volumes
+            }
+
+        except requests.exceptions.RequestException as e:
+            logger.error(f"HTTP error fetching candle data for {ticker}: {e}")
+            return None
+        except Exception as e:
+            logger.error(f"Error fetching candle data for {ticker}: {e}")
+            return None
+
+    def is_available(self) -> bool:
+        """
+        Check if Polygon API is accessible.
+
+        Returns:
+            True if accessible, False otherwise
+        """
+        try:
+            # Test with a simple request
+            test_data = self.get_candles("AAPL", days=5)
+            return test_data is not None
+        except Exception as e:
+            logger.error(f"Polygon API unavailable: {e}")
+            return False