CTAO Science Portal: static Astro site with git-based CMS (Sveltia + Gitea)

Portal code only; editorial content lives in the ctao/content repo on the
demo machine's Gitea and is overlaid at build time (see README.md and
deploy/README.md). Live demo: https://astro.isl-dev.grid.cyfronet.pl

public/robots.txt

@@ -0,0 +1,4 @@
+# Demo instance — keep out of search indexes until this becomes the real
+# portal on its final domain (then: Allow: / and restore the Sitemap line).
+User-agent: *
+Disallow: /