enhance security and performance: add rate limiting, session validation, and logging; update environment variables

src/utils/logger.js

@@ -0,0 +1,42 @@
+const fs = require('fs');
+const path = require('path');
+
+const logsDir = path.join(process.env.DATA_PATH || './data', 'logs');
+if (!fs.existsSync(logsDir)) {
+  fs.mkdirSync(logsDir, { recursive: true });
+}
+
+const logger = {
+  info: (message, meta = {}) => {
+    const logEntry = {
+      timestamp: new Date().toISOString(),
+      level: 'info',
+      message,
+      ...meta
+    };
+    console.log(JSON.stringify(logEntry));
+  },
+
+  error: (message, error = null, meta = {}) => {
+    const logEntry = {
+      timestamp: new Date().toISOString(),
+      level: 'error',
+      message,
+      error: error ? { message: error.message, stack: error.stack } : null,
+      ...meta
+    };
+    console.error(JSON.stringify(logEntry));
+  },
+
+  warn: (message, meta = {}) => {
+    const logEntry = {
+      timestamp: new Date().toISOString(),
+      level: 'warn',
+      message,
+      ...meta
+    };
+    console.warn(JSON.stringify(logEntry));
+  }
+};
+
+module.exports = logger;