Add cryptocurrency price command via CoinGecko API

New features:
- !crypto <SYMBOL> command to query cryptocurrency prices
- CoinGeckoAPI integration (free, no API key required)
- Support for 20+ popular cryptocurrencies (BTC, ETH, DOGE, etc.)
- 24-hour price change and volume data
- Colored embeds matching price movement
- Alias: !c for quick crypto queries

Uses CoinGecko's free /simple/price endpoint with 30 calls/min rate limit.

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

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

crypto_api.py

@@ -0,0 +1,113 @@
+import requests
+import logging
+from typing import Optional, Dict, Any
+
+logger = logging.getLogger(__name__)
+
+
+class CoinGeckoAPI:
+    """CoinGecko implementation for cryptocurrency price data."""
+
+    BASE_URL = "https://api.coingecko.com/api/v3"
+
+    # Common crypto symbol to CoinGecko ID mapping
+    SYMBOL_MAP = {
+        'BTC': 'bitcoin',
+        'ETH': 'ethereum',
+        'USDT': 'tether',
+        'BNB': 'binancecoin',
+        'SOL': 'solana',
+        'XRP': 'ripple',
+        'USDC': 'usd-coin',
+        'ADA': 'cardano',
+        'DOGE': 'dogecoin',
+        'TRX': 'tron',
+        'DOT': 'polkadot',
+        'MATIC': 'matic-network',
+        'LTC': 'litecoin',
+        'SHIB': 'shiba-inu',
+        'AVAX': 'avalanche-2',
+        'LINK': 'chainlink',
+        'UNI': 'uniswap',
+        'XLM': 'stellar',
+        'ATOM': 'cosmos',
+        'XMR': 'monero'
+    }
+
+    def get_crypto_price(self, symbol: str) -> Optional[Dict[str, Any]]:
+        """
+        Retrieve cryptocurrency price data from CoinGecko.
+
+        Args:
+            symbol: Crypto symbol (e.g., BTC, ETH, DOGE)
+
+        Returns:
+            Dictionary with crypto data or None if unavailable
+        """
+        try:
+            # Convert symbol to CoinGecko ID
+            symbol = symbol.upper()
+            coin_id = self.SYMBOL_MAP.get(symbol, symbol.lower())
+
+            # Fetch price data
+            url = f"{self.BASE_URL}/simple/price"
+            params = {
+                'ids': coin_id,
+                'vs_currencies': 'usd',
+                'include_24hr_change': 'true',
+                'include_24hr_vol': 'true',
+                'include_last_updated_at': 'true'
+            }
+
+            response = requests.get(url, params=params, timeout=10)
+            response.raise_for_status()
+            data = response.json()
+
+            if coin_id not in data:
+                logger.warning(f"No data available for crypto: {symbol}")
+                return None
+
+            crypto_data = data[coin_id]
+            current_price = crypto_data.get('usd', 0)
+            change_percent = crypto_data.get('usd_24h_change', 0)
+
+            if current_price == 0:
+                logger.warning(f"Invalid price data for crypto: {symbol}")
+                return None
+
+            # Calculate previous price from 24h change
+            change_decimal = change_percent / 100
+            previous_price = current_price / (1 + change_decimal)
+            change_dollar = current_price - previous_price
+
+            return {
+                'symbol': symbol,
+                'coin_id': coin_id,
+                'current_price': round(current_price, 2),
+                'previous_price': round(previous_price, 2),
+                'change_dollar': round(change_dollar, 2),
+                'change_percent': round(change_percent, 2),
+                'volume_24h': crypto_data.get('usd_24h_vol', 0)
+            }
+
+        except requests.exceptions.RequestException as e:
+            logger.error(f"Error fetching data for {symbol}: {e}")
+            return None
+        except Exception as e:
+            logger.error(f"Unexpected error fetching data for {symbol}: {e}")
+            return None
+
+    def is_available(self) -> bool:
+        """
+        Check if CoinGecko API is accessible.
+
+        Returns:
+            True if accessible, False otherwise
+        """
+        try:
+            url = f"{self.BASE_URL}/ping"
+            response = requests.get(url, timeout=5)
+            return response.status_code == 200
+        except Exception as e:
+            logger.error(f"CoinGecko API unavailable: {e}")
+            return False