Refactor API configuration and improve WebSocket handling in frontend and backend

frontend/src/pages/LoginPage.tsx

@@ -1,10 +1,9 @@
 import { useEffect } from 'react';
 import { useNavigate } from 'react-router-dom';
 import { useAuth } from '../contexts/AuthContext';
+import { API_BASE_URL } from '../config';
 import './LoginPage.css';
 
-const API_BASE_URL = import.meta.env.VITE_API_URL || "https://docnest-backend-mingda.fly.dev/api";
-
 function LoginPage() {
   const { user, loading } = useAuth();
   const navigate = useNavigate();