feat(deploy): hash the per-site artifact set and stamp it on a successful artifact deploy

ArtifactRevisionHashService (deterministic SHA-256 of the per-site
DeployArtifactsCommand, DeploymentId/timestamp excluded) stamps
Site.ArtifactRevisionHash/ArtifactsDeployedAt for every site whose deploy
succeeded; failed sites keep their previous stamp.
ComputeCurrentArtifactHashesAsync answers "what would it be now".

Claude-Session: https://claude.ai/code/session_01Y5ef34iUUMjmwnMpL9xgmB

tests/ZB.MOM.WW.ScadaBridge.CentralUI.Tests/Admin/SitesPageTests.cs

@@ -44,7 +44,8 @@ public class SitesPageTests : BunitContext
             comms,
             Substitute.For<IAuditService>(),
             Options.Create(new DeploymentManagerOptions()),
-            NullLogger<ArtifactDeploymentService>.Instance);
+            NullLogger<ArtifactDeploymentService>.Instance,
+            new ArtifactRevisionHashService());
         Services.AddSingleton(artifactSvc);
 
         Services.AddSingleton<IDialogService>(Substitute.For<IDialogService>());