feat(seo): add sitemap

src/robots.txt

@@ -1,3 +1,5 @@
+Sitemap: https://www.astrolabe.coop/sitemap.xml
+
 User-agent: *
 Disallow: /fonts/
 Disallow: /form/

src/sitemap.njk

@@ -0,0 +1,13 @@
+---
+permalink: /sitemap.xml
+eleventyExcludeFromCollections: true
+---
+<?xml version="1.0" encoding="utf-8"?>
+<urlset xmlns="http://www.sitemaps.org/schemas/sitemap/0.9">
+    {% for page in collections.all %}
+        <url>
+            <loc>{{ site.url }}{{ page.url | url }}</loc>
+            <lastmod>{{ page.date.toISOString() }}</lastmod>
+        </url>
+    {% endfor %}
+</urlset>