chore: Secure secrets and add MySQL deps

.env.example

@@ -30,3 +30,10 @@ API_HOST=0.0.0.0
 
 # Classification Threshold
 PRICE_CHANGE_THRESHOLD=0.015  # 1.5% threshold for binary labels
+
+# MySQL Configuration
+MYSQL_HOST=localhost
+MYSQL_PORT=3306
+MYSQL_USER=user
+MYSQL_PASSWORD=password
+MYSQL_DB=crypto_predictor