Declare AI content usage preferences in robots.txt

Add Content-Signal directive opting in to AI training, search indexing,
and AI input (RAG/grounding). Docker's official docs benefit from wide
distribution through AI assistants, so permitting training and grounding
is aligned with the site's purpose.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

layouts/home.robots.txt

@@ -7,6 +7,7 @@
 {{- if hugo.IsProduction -}}
 User-agent: *
 Disallow: /unassociated-machines/
+Content-Signal: ai-train=yes, search=yes, ai-input=yes
 
 
 Sitemap: {{ "sitemap.xml" | absURL }}