feat(seo): add sitemap.xml + robots.txt to surface dataset downloads to crawlers

Author: iPythoning

robots.txt

@@ -0,0 +1,4 @@
+User-agent: *
+Allow: /
+
+Sitemap: https://ipythoning.github.io/lien-deadlines/sitemap.xml

sitemap.xml

@@ -0,0 +1,21 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<urlset xmlns="http://www.sitemaps.org/schemas/sitemap/0.9">
+  <url>
+    <loc>https://ipythoning.github.io/lien-deadlines/</loc>
+    <lastmod>2026-06-10</lastmod>
+    <changefreq>monthly</changefreq>
+    <priority>1.0</priority>
+  </url>
+  <url>
+    <loc>https://ipythoning.github.io/lien-deadlines/data/deadlines.json</loc>
+    <lastmod>2026-06-10</lastmod>
+    <changefreq>monthly</changefreq>
+    <priority>0.8</priority>
+  </url>
+  <url>
+    <loc>https://ipythoning.github.io/lien-deadlines/data/deadlines.csv</loc>
+    <lastmod>2026-06-10</lastmod>
+    <changefreq>monthly</changefreq>
+    <priority>0.8</priority>
+  </url>
+</urlset>