feat: add sitemap.xml, robots.txt, and page discovery metadata

The site returned index.html for both /robots.txt and /sitemap.xml because
the Workers Assets SPA fallback served the app shell with text/html, so
crawlers got a page instead of either file.

The site is a single document: About/Projects/Skills/Links are windows, not
URLs, and there is no hash or pushState routing. The sitemap therefore lists
the one real URL rather than inventing paths that 404.

Also adds the description, canonical, and og: tags the head was missing.

index.html

@@ -4,6 +4,12 @@
   <meta charset="UTF-8">
   <meta name="viewport" content="width=device-width, initial-scale=1.0">
   <title>katOS — oiupoyt</title>
+  <meta name="description" content="Terminal desktop portfolio of oiupoyt: draggable windows, a working shell, fastfetch, and links to projects and websites.">
+  <link rel="canonical" href="https://oiupoyt.space/">
+  <meta property="og:type" content="website">
+  <meta property="og:url" content="https://oiupoyt.space/">
+  <meta property="og:title" content="katOS — oiupoyt">
+  <meta property="og:description" content="Terminal desktop portfolio of oiupoyt: draggable windows, a working shell, fastfetch, and links to projects and websites.">
 
   <!-- Google AdSense -->
   <script async src="https://pagead2.googlesyndication.com/pagead/js/adsbygoogle.js?client=ca-pub-3876936176422477" crossorigin="anonymous"></script>

robots.txt

@@ -0,0 +1,4 @@
+User-agent: *
+Allow: /
+
+Sitemap: https://oiupoyt.space/sitemap.xml

sitemap.xml

@@ -0,0 +1,9 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<urlset xmlns="http://www.sitemaps.org/schemas/sitemap/0.9">
+  <url>
+    <loc>https://oiupoyt.space/</loc>
+    <lastmod>2026-10-19</lastmod>
+    <changefreq>weekly</changefreq>
+    <priority>1.0</priority>
+  </url>
+</urlset>