Add matplotlib-based chart generation with Yahoo Finance data

- Add chart_generator.py with price and candlestick chart support
- Implement Yahoo Finance candle data fetching for free historical data
- Update bot to generate and attach charts to stock embeds
- Add matplotlib dependency to requirements.txt
- Configure dual API approach: Finnhub for quotes, Yahoo for charts

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

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

stock_api/finnhub_api.py

@@ -1,8 +1,8 @@
 import finnhub
 import logging
-from typing import Optional, Dict, Any
+from typing import Optional, Dict, Any, List
 from .base import StockAPIBase
-from datetime import datetime
+from datetime import datetime, timedelta
 import pytz
 
 
@@ -170,3 +170,40 @@ class FinnhubAPI(StockAPIBase):
         except Exception as e:
             logger.error(f"Error fetching earnings calendar: {e}")
             return None
+
+    def get_candles(self, ticker: str, days: int = 30, resolution: str = 'D') -> Optional[Dict[str, List]]:
+        """
+        Retrieve historical candlestick data from Finnhub.
+
+        Args:
+            ticker: Stock ticker symbol
+            days: Number of days of historical data to fetch
+            resolution: Candle resolution (1, 5, 15, 30, 60, D, W, M)
+
+        Returns:
+            Dictionary with OHLCV data or None if unavailable
+        """
+        try:
+            # Calculate timestamps
+            end_time = int(datetime.now().timestamp())
+            start_time = int((datetime.now() - timedelta(days=days)).timestamp())
+
+            # Fetch candle data
+            candles = self.client.stock_candles(ticker, resolution, start_time, end_time)
+
+            if not candles or candles.get('s') != 'ok':
+                logger.warning(f"No candle data available for ticker: {ticker}")
+                return None
+
+            return {
+                'timestamps': candles['t'],
+                'open': candles['o'],
+                'high': candles['h'],
+                'low': candles['l'],
+                'close': candles['c'],
+                'volume': candles['v']
+            }
+
+        except Exception as e:
+            logger.error(f"Error fetching candle data for {ticker}: {e}")
+            return None