Drop the demo.lumbridgecorp.com alias; one hostname

The site is demo.primeintellectgrowth.com and nothing else. The Caddy block,
the deploy smoke test, the mirrored Caddyfile and the docs all carried the
second name; all four no longer do.

deploy/Caddyfile.demo

@@ -1,10 +1,7 @@
 # The live block on cloud-2, kept here so the config is reviewable in the repo.
 # Copy of /etc/caddy/Caddyfile's demo section — if you change one, change both.
 
-# Both names serve the same build from the same root. The prerendered HTML
-# carries <link rel=canonical> pointing at the primeintellectgrowth name, so
-# the second hostname does not split search ranking between two copies.
-demo.primeintellectgrowth.com, demo.lumbridgecorp.com {
+demo.primeintellectgrowth.com {
 	# REQUIRED, and its absence is silent. Without it Caddy builds a second
 	# server on *:443 that has never heard of this hostname, and public traffic
 	# — which NATs to 10.0.0.2 — falls through to an empty 200 behind a