refactor(deployment): move PendingUpdatesCache to DeploymentManager so the CLI shares it (ScadaBridge#91)

`health pending-updates` (#63) called IPendingUpdatesEvaluator.EvaluateAsync directly
from ManagementActor because the cache lived in CentralUI, so every CLI call was a full
uncached fleet flatten. IPendingUpdatesCache/PendingUpdatesCache now live in
DeploymentManager.PendingUpdates and are registered by AddDeploymentManager; the
SingleFlightMemo<T> primitive moves to Commons.Caching (public) so both CentralUI's KPI /
alarm-summary caches and DeploymentManager can use it. HandleGetPendingUpdates reads the
shared cache; the UI circuits and the CLI now share one memo per node.

Tests: ManagementActor repeated-calls test (fails against the direct evaluator call:
2 evaluations instead of 1), AddDeploymentManager singleton-registration test; the cache
and memo tests move with their types.

(ScadaBridge#91)

Claude-Session: https://claude.ai/code/session_01GT67AEHd2Acv1YPwGfXEoV

tests/ZB.MOM.WW.ScadaBridge.DeploymentManager.Tests/ServiceCollectionExtensionsTests.cs

@@ -81,4 +81,26 @@ public class ServiceCollectionExtensionsTests
         Assert.IsType<DeploymentStatusNotifier>(fromRoot);
         Assert.Same(fromRoot, fromScope);
     }
+
+    /// <summary>
+    /// Gitea #91: the pending-updates cache is registered by AddDeploymentManager (not the
+    /// Central UI) as ONE process-wide singleton, so the UI circuits and the management API's
+    /// GetPendingUpdatesCommand share a single memo.
+    /// </summary>
+    [Fact]
+    public void AddDeploymentManager_RegistersPendingUpdatesCache_AsSingleton()
+    {
+        var services = new ServiceCollection();
+        services.AddLogging();
+        services.AddDeploymentManager();
+
+        using var provider = services.BuildServiceProvider();
+
+        var fromRoot = provider.GetRequiredService<PendingUpdates.IPendingUpdatesCache>();
+        using var scope = provider.CreateScope();
+        var fromScope = scope.ServiceProvider.GetRequiredService<PendingUpdates.IPendingUpdatesCache>();
+
+        Assert.IsType<PendingUpdates.PendingUpdatesCache>(fromRoot);
+        Assert.Same(fromRoot, fromScope);
+    }
 }