fix(ui): disposal guard on Alarm Summary live callback, matching the DebugView pattern (plan R2-07 T9)

src/ZB.MOM.WW.ScadaBridge.CentralUI/Components/Pages/Monitoring/AlarmSummary.razor

@@ -382,15 +382,20 @@
         _liveSubscription = null;
     }
 
+    // N7: set BEFORE teardown so a live callback racing Dispose is dropped both
+    // before the InvokeAsync marshal and inside it (mirrors DebugView.razor).
+    private volatile bool _disposed;
+
     // Raised on the aggregator's thread — marshal onto the circuit before touching state.
     private void OnLiveAlarmsChanged(int siteId)
     {
+        if (_disposed) return;
         _ = InvokeAsync(() =>
         {
             // Drop stale callbacks for a site we've since navigated away from, and
             // let the poll drive until the aggregator has actually seeded (so we never
             // clobber a good poll snapshot with an empty pre-seed list).
-            if (_selectedSiteId != siteId || !LiveAlarmCache.IsLive(siteId))
+            if (_disposed || _selectedSiteId != siteId || !LiveAlarmCache.IsLive(siteId))
             {
                 return;
             }
@@ -525,6 +530,7 @@
 
     public void Dispose()
     {
+        _disposed = true;
         StopTimer();
         DisposeLiveSubscription();
     }