feat(web): add same-origin SPA authentication

apps/web/src/lib/socket.ts

@@ -1,12 +1,10 @@
 import { io, type Socket } from 'socket.io-client';
 
-const GATEWAY_URL = process.env['NEXT_PUBLIC_GATEWAY_URL'] ?? 'http://localhost:14242';
-
 let socket: Socket | null = null;
 
 export function getSocket(): Socket {
   if (!socket) {
-    socket = io(`${GATEWAY_URL}/chat`, {
+    socket = io('/chat', {
       withCredentials: true,
       autoConnect: false,
       transports: ['websocket', 'polling'],