Add Bluesky link.

Author: t-paul

advent-calendar-2025/index.html

@@ -521,6 +521,7 @@
       <br><span class="gray small">Advent Calendar 2025</span>
       <br><span class="gray small">#SCADvent &nbsp;
       <a class="gray" href="https://fosstodon.org/@OpenSCAD" title="Mastodon" rel="me"><i class="fab fa-mastodon"></i></a>
+      <a class="gray" href="https://bsky.app/profile/openscad.bsky.social" title="Bluesky" rel="me"><i class="fab fa-bluesky"></i></a>
       </span>
       <img src="https://openscad.org/images/openscad.png">
     </p>