feat(site): artifact apply writes deployed secrets and answers SecretsApplied

tests/ZB.MOM.WW.ScadaBridge.SiteRuntime.Tests/Secrets/DeployedSecretsMirrorTests.cs

@@ -333,6 +333,9 @@ public class DeployedSecretsMirrorTests : IDisposable
         var message = Assert.Single(r.Failed);
         Assert.Contains("kek-central", message);
         Assert.Contains("'a'", message);
+        // FailedNames (Task 10): the name behind each Failed entry, in lockstep order, so a
+        // caller (DeploymentManagerActor) can tell whether a failure belongs to names it shipped.
+        Assert.Equal(["a"], r.FailedNames);
     }
 
     [Fact]