fix(seo): serve sitemap and preserve static metadata files

public/robots.txt

@@ -1,6 +1,7 @@
 # https://www.robotstxt.org/robotstxt.html
 User-agent: *
 Disallow:
+Sitemap: https://5chan.app/sitemap.xml
 
 # 5chan — open-source decentralized imageboard
 # Source: https://github.com/bitsocialhq/5chan

public/sitemap.xml

@@ -0,0 +1,6 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<urlset xmlns="http://www.sitemaps.org/schemas/sitemap/0.9">
+  <url>
+    <loc>https://5chan.app/</loc>
+  </url>
+</urlset>

vercel.json

@@ -1,6 +1,6 @@
 {
   "rewrites": [
-    { "source": "/(.*)", "destination": "/index.html" }
+    { "source": "^/(?!.*\\.).*$", "destination": "/index.html" }
   ],
   "headers": [
     {