fix: environment variable API_URL can't be changed

frontend/src/pages/api/[...all].tsx

@@ -1,6 +1,5 @@
 import { NextApiRequest, NextApiResponse } from "next";
 import httpProxyMiddleware from "next-http-proxy-middleware";
-import getConfig from "next/config";
 
 export const config = {
   api: {
@@ -9,7 +8,7 @@ export const config = {
   },
 };
 
-const { apiURL } = getConfig().serverRuntimeConfig;
+const apiURL = process.env.API_URL || "http://localhost:8080";
 
 // A proxy to the API server only used in development.
 // In production this route gets overridden by Caddy.