bingo: serve bingo.asxp.io too, credit asxp.io in footer

datacenterbingo.xyz is not in the .xyz zone yet, while bingo.asxp.io
already resolves. Serve the card on both (BINGO_ALT_HOST) so it is
reachable now; canonical and hreflang links keep pointing at the .xyz
domain. Footer gets a copyright line linking back to asxp.io.

Assisted-by: Claude:opus-5

views/bingo/index.erb

@@ -62,7 +62,10 @@
     </ul>
   </section>
 
-  <footer><%= t(:footer) %></footer>
+  <footer>
+    <p><%= t(:footer) %></p>
+    <p>© <%= Date.today.year %> <a href="https://asxp.io">asxp.io</a></p>
+  </footer>
 </main>
 
 <% b.cells.each do |dc| %>

views/bingo/layout.erb

@@ -93,6 +93,7 @@
   dialog ul { padding-left: 18px; }
   dialog button { font: inherit; padding: 6px 14px; border-radius: 6px; border: 1px solid var(--line); background: var(--bg); color: var(--ink); cursor: pointer; }
   footer { margin-top: 32px; color: var(--muted); font-size: 13px; }
+  footer p { margin: 0 0 4px; }
   @media (max-width: 560px) {
     .cell { padding: 5px; border-radius: 6px; }
     .cell .sub, .cell .n, .cell .tag { display: none; }