feat: update sitemap and robots.txt for new routes

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

public/robots.txt

@@ -1,4 +1,5 @@
 User-agent: *
 Allow: /
+Disallow: /app
 
 Sitemap: https://texpixel.com/sitemap.xml

public/sitemap.xml

@@ -3,11 +3,35 @@
         xmlns:xhtml="http://www.w3.org/1999/xhtml">
   <url>
     <loc>https://texpixel.com/</loc>
-    <lastmod>2026-03-11</lastmod>
+    <lastmod>2026-03-25</lastmod>
     <changefreq>weekly</changefreq>
     <priority>1.0</priority>
     <xhtml:link rel="alternate" hreflang="zh-CN" href="https://texpixel.com/"/>
     <xhtml:link rel="alternate" hreflang="en" href="https://texpixel.com/"/>
     <xhtml:link rel="alternate" hreflang="x-default" href="https://texpixel.com/"/>
   </url>
+  <url>
+    <loc>https://texpixel.com/docs</loc>
+    <lastmod>2026-03-25</lastmod>
+    <changefreq>weekly</changefreq>
+    <priority>0.8</priority>
+  </url>
+  <url>
+    <loc>https://texpixel.com/docs/getting-started</loc>
+    <lastmod>2026-03-25</lastmod>
+    <changefreq>monthly</changefreq>
+    <priority>0.7</priority>
+  </url>
+  <url>
+    <loc>https://texpixel.com/blog</loc>
+    <lastmod>2026-03-25</lastmod>
+    <changefreq>weekly</changefreq>
+    <priority>0.8</priority>
+  </url>
+  <url>
+    <loc>https://texpixel.com/blog/introducing-texpixel</loc>
+    <lastmod>2026-03-25</lastmod>
+    <changefreq>monthly</changefreq>
+    <priority>0.6</priority>
+  </url>
 </urlset>