perf(ui): shared KPI cache, live-cache-backed alarm summary, coalesced debug renders

tests/ZB.MOM.WW.ScadaBridge.CentralUI.Tests/Pages/HealthPageTests.cs

@@ -64,6 +64,14 @@ public class HealthPageTests : BunitContext
         _comms.SetSiteCallAudit(siteCallAudit);
         Services.AddSingleton(_comms);
 
+        // arch-review WP2.4 — the page no longer queries CommunicationService /
+        // IAuditLogQueryService per circuit; it reads the process-level memoized
+        // KPI cache. The real cache is registered here (not a substitute) so the
+        // scripted-actor seam above is still what actually answers.
+        Services.AddSingleton<IKpiSnapshotCache>(sp => new KpiSnapshotCache(
+            sp.GetRequiredService<CommunicationService>(),
+            sp.GetRequiredService<IServiceScopeFactory>()));
+
         var aggregator = Substitute.For<ICentralHealthAggregator>();
         aggregator.GetAllSiteStates()
             .Returns(new Dictionary<string, SiteHealthState>());