bingo: put the topic in the h1

The h1 was just the brand ("Datacenter Bingo"), so the page's main
heading carried none of the terms people search for. Add a per-locale
tagline inside the h1 and shorten the lead paragraph so it no longer
repeats it.

Assisted-by: Claude:opus-5

views/bingo/index.erb

@@ -1,7 +1,7 @@
 <% b = @board %>
 <main>
   <header>
-    <h1><%= t(:lead) %> <span><%= t(:accent) %></span></h1>
+    <h1><%= t(:lead) %> <span><%= t(:accent) %></span> <small><%= t(:tagline) %></small></h1>
     <div class="switches">
       <nav class="toggle" aria-label="<%= t(:view_label) %>">
         <% Bingo::VIEWS.each do |v| %>