feat(alarm-summary): live-cache-driven updates with poll fallback (plan #10 T5)

Wire the operator Alarm Summary page to the transient per-site live alarm
cache (ISiteAlarmLiveCache, T4). Live-cache-first: on site select the page
subscribes and rebuilds rows/rollup from near-real-time onChanged deltas; the
15s poll is kept untouched as the authority for NotReporting and as the
safety net whenever the cache is not live (pre-seed or degraded stream). Both
paths mutate shared state only via the Blazor dispatcher, so they never race,
and each rebuild is an idempotent snapshot.

- IAlarmSummaryService.BuildFromLiveAlarms: flattens a live AlarmStateChanged
  snapshot to AlarmSummaryRows with the same deterministic instance-then-name
  sort as GetSiteAlarmsAsync; NotReporting always empty on the live path.
- AlarmSummary.razor: inject ISiteAlarmLiveCache; subscribe on select,
  re-subscribe on site change, unsubscribe on leave + Dispose.
- Tests: service BuildFromLiveAlarms flatten/sort/empty; page subscribe,
  poll-fallback render, onChanged rebuild, unsubscribe on leave/change/dispose.

Claude-Session: https://claude.ai/code/session_01MtdgwpEeCUn6cUA5f1LMPj

src/ZB.MOM.WW.ScadaBridge.CentralUI/Services/AlarmSummaryService.cs

@@ -127,6 +127,26 @@ public sealed class AlarmSummaryService : IAlarmSummaryService
         }
     }
 
+    /// <inheritdoc/>
+    public AlarmSummaryResult BuildFromLiveAlarms(IReadOnlyList<AlarmStateChanged> alarms)
+    {
+        ArgumentNullException.ThrowIfNull(alarms);
+
+        // Flatten one row per alarm (instance from the alarm itself, mirroring
+        // FetchInstanceAsync) and apply the SAME deterministic instance-then-name
+        // sort as GetSiteAlarmsAsync so the live and poll paths render identically.
+        var orderedRows = alarms
+            .Select(alarm => new AlarmSummaryRow(alarm.InstanceUniqueName, alarm))
+            .OrderBy(r => r.InstanceUniqueName, StringComparer.OrdinalIgnoreCase)
+            .ThenBy(r => r.Alarm.AlarmName, StringComparer.OrdinalIgnoreCase)
+            .ToList();
+
+        // The live cache is alarm-only, so it cannot enumerate "not reporting"
+        // instances — left empty here; the periodic poll (GetSiteAlarmsAsync)
+        // remains the authority for that list.
+        return new AlarmSummaryResult(orderedRows, Array.Empty<string>());
+    }
+
     /// <inheritdoc/>
     public AlarmRollup ComputeRollup(IReadOnlyList<AlarmSummaryRow> rows)
     {