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>

chart_generator.py

@@ -0,0 +1,162 @@
+import matplotlib
+matplotlib.use('Agg')
+import matplotlib.pyplot as plt
+import matplotlib.dates as mdates
+from datetime import datetime
+from typing import Dict, List, Optional
+import logging
+import io
+
+logger = logging.getLogger(__name__)
+
+
+class ChartGenerator:
+    """Generates stock price charts using matplotlib."""
+
+    @staticmethod
+    def create_price_chart(
+        ticker: str,
+        candle_data: Dict[str, List],
+        company_name: Optional[str] = None
+    ) -> Optional[io.BytesIO]:
+        """
+        Create a price chart from candle data.
+
+        Args:
+            ticker: Stock ticker symbol
+            candle_data: Dictionary with timestamps, open, high, low, close, volume
+            company_name: Optional company name for title
+
+        Returns:
+            BytesIO buffer containing the chart image, or None if error
+        """
+        try:
+            # Convert timestamps to datetime objects
+            dates = [datetime.fromtimestamp(ts) for ts in candle_data['timestamps']]
+            closes = candle_data['close']
+
+            # Create figure and axis
+            fig, ax = plt.subplots(figsize=(12, 6), facecolor='#1e1e1e')
+            ax.set_facecolor('#2d2d2d')
+
+            # Plot closing prices
+            ax.plot(dates, closes, color='#00d4ff', linewidth=2)
+
+            # Fill area under the line
+            ax.fill_between(dates, closes, alpha=0.3, color='#00d4ff')
+
+            # Format x-axis
+            ax.xaxis.set_major_formatter(mdates.DateFormatter('%m/%d'))
+            ax.xaxis.set_major_locator(mdates.AutoDateLocator())
+            plt.xticks(rotation=45, ha='right')
+
+            # Grid styling
+            ax.grid(True, alpha=0.2, color='#ffffff', linestyle='-', linewidth=0.5)
+
+            # Labels and title
+            title = f"{company_name} ({ticker})" if company_name else ticker
+            ax.set_title(title, color='#ffffff', fontsize=14, fontweight='bold', pad=20)
+            ax.set_xlabel('Date', color='#ffffff', fontsize=10)
+            ax.set_ylabel('Price ($)', color='#ffffff', fontsize=10)
+
+            # Tick colors
+            ax.tick_params(colors='#ffffff', which='both')
+
+            # Spine colors
+            for spine in ax.spines.values():
+                spine.set_color('#444444')
+
+            # Tight layout
+            plt.tight_layout()
+
+            # Save to buffer
+            buffer = io.BytesIO()
+            plt.savefig(buffer, format='png', facecolor='#1e1e1e', dpi=100)
+            buffer.seek(0)
+            plt.close(fig)
+
+            return buffer
+
+        except Exception as e:
+            logger.error(f"Error generating chart for {ticker}: {e}")
+            return None
+
+    @staticmethod
+    def create_candlestick_chart(
+        ticker: str,
+        candle_data: Dict[str, List],
+        company_name: Optional[str] = None
+    ) -> Optional[io.BytesIO]:
+        """
+        Create a candlestick chart from candle data.
+
+        Args:
+            ticker: Stock ticker symbol
+            candle_data: Dictionary with timestamps, open, high, low, close, volume
+            company_name: Optional company name for title
+
+        Returns:
+            BytesIO buffer containing the chart image, or None if error
+        """
+        try:
+            # Convert timestamps to datetime objects
+            dates = [datetime.fromtimestamp(ts) for ts in candle_data['timestamps']]
+            opens = candle_data['open']
+            highs = candle_data['high']
+            lows = candle_data['low']
+            closes = candle_data['close']
+
+            # Create figure and axis
+            fig, ax = plt.subplots(figsize=(12, 6), facecolor='#1e1e1e')
+            ax.set_facecolor('#2d2d2d')
+
+            # Calculate bar width
+            width = 0.6
+
+            # Plot candlesticks
+            for i in range(len(dates)):
+                color = '#00ff88' if closes[i] >= opens[i] else '#ff4444'
+
+                # High-low line
+                ax.plot([dates[i], dates[i]], [lows[i], highs[i]], color=color, linewidth=1)
+
+                # Open-close rectangle
+                height = abs(closes[i] - opens[i])
+                bottom = min(opens[i], closes[i])
+                ax.bar(dates[i], height, width, bottom=bottom, color=color, alpha=0.8)
+
+            # Format x-axis
+            ax.xaxis.set_major_formatter(mdates.DateFormatter('%m/%d'))
+            ax.xaxis.set_major_locator(mdates.AutoDateLocator())
+            plt.xticks(rotation=45, ha='right')
+
+            # Grid styling
+            ax.grid(True, alpha=0.2, color='#ffffff', linestyle='-', linewidth=0.5)
+
+            # Labels and title
+            title = f"{company_name} ({ticker})" if company_name else ticker
+            ax.set_title(title, color='#ffffff', fontsize=14, fontweight='bold', pad=20)
+            ax.set_xlabel('Date', color='#ffffff', fontsize=10)
+            ax.set_ylabel('Price ($)', color='#ffffff', fontsize=10)
+
+            # Tick colors
+            ax.tick_params(colors='#ffffff', which='both')
+
+            # Spine colors
+            for spine in ax.spines.values():
+                spine.set_color('#444444')
+
+            # Tight layout
+            plt.tight_layout()
+
+            # Save to buffer
+            buffer = io.BytesIO()
+            plt.savefig(buffer, format='png', facecolor='#1e1e1e', dpi=100)
+            buffer.seek(0)
+            plt.close(fig)
+
+            return buffer
+
+        except Exception as e:
+            logger.error(f"Error generating candlestick chart for {ticker}: {e}")
+            return None