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.

test/test_app.rb

@@ -7,7 +7,7 @@ class AppTest < Minitest::Test
   def test_health
     response = request.get("/api/health")
     assert_equal 200, response.status
-    assert_equal({ "status" => "ok" }, json_body(response))
+    assert_equal({ "status" => "ok", "revision" => "dev" }, json_body(response))
   end
 
   def test_index_renders_with_asset_versioning_and_importmap