Fix DNS resolution for upstream API proxy

Node's built-in DNS resolver (c-ares) can fail to resolve hostnames
that the system resolver handles fine. Set dns.setDefaultResultOrder
to use the system resolver order.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend/src/index.ts

@@ -1,4 +1,7 @@
 import 'dotenv/config';
+import dns from 'node:dns';
+// Use system DNS resolver instead of Node's built-in c-ares resolver
+dns.setDefaultResultOrder('verbatim');
 import express from 'express';
 import cors from 'cors';
 import { verifyJwt } from './jwt.js';