Check the deployed revision, not just any 200, in the health poll

/api/health now reports REVISION alongside status, and the CI wait
step checks for this deploy's own short SHA specifically - a stray
old container that never got torn down (or a build that silently
kept serving stale code) would still 200 on a plain health check but
now won't match.

app.rb

@@ -169,7 +169,7 @@ module Maptool
     end
 
     get "/api/health" do
-      json status: "ok"
+      json status: "ok", revision: REVISION
     end
 
     get "/api/offline-tiles" do