perf: SEO optimalizations

Author: NkD

public/robots.txt

@@ -0,0 +1,4 @@
+User-agent: *
+Allow: /
+
+Sitemap: https://www.cuberact.org/sitemap-index.xml

src/layouts/BaseLayout.astro

@@ -26,6 +26,12 @@ const canonicalURL = new URL(Astro.url.pathname, Astro.site);
     <meta property="og:description" content={description} />
     <meta property="og:image" content={new URL('/images/cuberact-dark.png', Astro.site)} />
     <meta property="og:type" content="website" />
+    <meta property="og:url" content={canonicalURL} />
+    <meta name="twitter:card" content="summary_large_image" />
+    <meta name="twitter:site" content="@cuberact" />
+    <meta name="twitter:title" content={title} />
+    <meta name="twitter:description" content={description} />
+    <meta name="twitter:image" content={new URL('/images/cuberact-dark.png', Astro.site)} />
     <title>{title}</title>
     <script defer src="https://cloud.umami.is/script.js" data-website-id="1b1cb958-7e25-4fb3-82ee-28ca7951c7b3"></script>
   </head>