🐛 fix: fix sitemap config

Author: arvinxx

.gitignore

@@ -57,3 +57,5 @@ next-env.d.ts
 public/*.js
 bun.lockb
 sitemap*.xml
+robots.txt
+

next-sitemap.config.mjs

@@ -2,11 +2,9 @@ import { glob } from 'glob';
 
 const isVercelPreview = process.env.VERCEL === '1' && process.env.VERCEL_ENV !== 'production';
 
-const prodUrl = process.env.SITE_URL || 'https://chat-preview.lobehub.com';
-
 const vercelPreviewUrl = `https://${process.env.VERCEL_URL}`;
 
-const siteUrl = isVercelPreview ? vercelPreviewUrl : prodUrl;
+const siteUrl = isVercelPreview ? vercelPreviewUrl : 'https://chat-preview.lobehub.com';
 
 /** @type {import('next-sitemap').IConfig} */
 const config = {
@@ -49,6 +47,7 @@ const config = {
     return paths;
   },
   siteUrl,
+  generateRobotsTxt: true,
 };
 
 export default config;