fix: use relative URLs for API endpoints in production

Changed auth service to use relative URLs (empty API_URL prefix) when
VITE_API_URL is not set. This allows nginx to properly proxy requests
in production deployments where the frontend and API are served from
the same domain.

Previously, the Google OAuth redirect would try to connect to
localhost:3001 which is not accessible from the browser. Now it uses
/api/auth/google which nginx proxies to the API container.

This fix enables proper authentication flow in production while
maintaining development functionality with explicit VITE_API_URL.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

packages/web/src/services/auth.service.ts

@@ -13,7 +13,9 @@ import {
   ResetPasswordRequest,
 } from '../types/auth';
 
-const API_URL = (import.meta as any).env?.VITE_API_URL || 'http://localhost:3001';
+// Use relative URL in production (when VITE_API_URL is not set)
+// This allows nginx to proxy requests properly
+const API_URL = (import.meta as any).env?.VITE_API_URL || '';
 const AUTH_ENDPOINT = `${API_URL}/api/auth`;
 
 // Token storage keys