fix: drop noreferrer from footer menu external links to preserve Umami referral tracking

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

layouts/partials/footer.html

@@ -27,7 +27,7 @@
               <a
                 href="{{ .URL }}"
                 target="_blank"
-                rel="noopener noreferrer"
+                rel="noopener"
                 class="label text-fog hover:text-heat transition-colors"
               >
                 {{- .Name -}}{{ partial "icon.html" "arrow-external" }}