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

config.ru

@@ -2,16 +2,19 @@ require 'sinatra/base'
 require './asxpio.rb'
 require './bingo_web.rb'
 
-# One process, two sites: BINGO_HOST gets the bingo, everything else asxp.io.
-asxpio     = AsxpioWeb.new
-bingo      = BingoWeb.new
-bingo_host = ENV['BINGO_HOST']
+# One process, two sites: the bingo hosts get BingoWeb, everything else
+# asxp.io. BINGO_HOST is canonical (www. redirects to it); BINGO_ALT_HOST
+# serves the same card, e.g. while the canonical domain's DNS settles.
+asxpio      = AsxpioWeb.new
+bingo       = BingoWeb.new
+bingo_host  = ENV['BINGO_HOST']
+bingo_hosts = BingoWeb::HOSTS
 
 run lambda { |env|
   req = Rack::Request.new(env)
   if bingo_host && req.host == "www.#{bingo_host}"
     [301, { 'location' => "https://#{bingo_host}#{req.fullpath}" }, []]
   else
-    (bingo_host && req.host == bingo_host ? bingo : asxpio).call(env)
+    (bingo_hosts.include?(req.host) ? bingo : asxpio).call(env)
   end
 }