Add sitemap.xml and fix Nginx routing for SEO files

- Create public/sitemap.xml with all public routes (/, /terms, /privacy, /login)
- Add Sitemap directive to robots.txt
- Add explicit Nginx location block for /sitemap.xml with application/xml content type
- Harden robots.txt Nginx block with try_files and explicit text/plain type
- Prevents SPA fallback from serving index.html for /sitemap.xml

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

Author: Programcode

nginx.conf

@@ -21,9 +21,17 @@ server {
         add_header Cache-Control "no-store, no-cache, must-revalidate, proxy-revalidate, max-age=0";
     }
 
-    # Allow robots.txt
+    # SEO: Serve robots.txt and sitemap.xml directly (bypass SPA fallback and .txt block)
     location = /robots.txt {
         allow all;
+        default_type text/plain;
+        try_files $uri =404;
+    }
+
+    location = /sitemap.xml {
+        allow all;
+        default_type application/xml;
+        try_files $uri =404;
     }
 
     # SECURITY: Block access to sensitive files

public/robots.txt

@@ -12,3 +12,5 @@ Allow: /
 
 User-agent: *
 Allow: /
+
+Sitemap: https://debate.pi-stack.org/sitemap.xml

public/sitemap.xml

@@ -0,0 +1,23 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<urlset xmlns="http://www.sitemaps.org/schemas/sitemap/0.9">
+  <url>
+    <loc>https://debate.pi-stack.org/</loc>
+    <changefreq>weekly</changefreq>
+    <priority>1.0</priority>
+  </url>
+  <url>
+    <loc>https://debate.pi-stack.org/terms</loc>
+    <changefreq>monthly</changefreq>
+    <priority>0.3</priority>
+  </url>
+  <url>
+    <loc>https://debate.pi-stack.org/privacy</loc>
+    <changefreq>monthly</changefreq>
+    <priority>0.3</priority>
+  </url>
+  <url>
+    <loc>https://debate.pi-stack.org/login</loc>
+    <changefreq>monthly</changefreq>
+    <priority>0.5</priority>
+  </url>
+</urlset>