feat(streaming): carry AckTime on DebugAlarmStateDto (21) (ScadaBridge#84)

The live AlarmStateUpdate already carried ack_time (24) but the Debug View
snapshot DTO did not, so snapshot-seeded alarm rows showed a null ack time
until the next live update. Additive google.protobuf.Timestamp ack_time = 21
(absent => null, including from a pre-#84 site), vendored C# regenerated with
docker/regen-proto.sh sitecommand, mapped both ways in SiteCommandDtoMapper.
The native golden sample now sets AckTime (the computed one leaves it null),
so the round-trip golden pins both the present and the absent decode.

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

src/ZB.MOM.WW.ScadaBridge.Communication/Grpc/SiteCommandDtoMapper.cs

@@ -1955,6 +1955,11 @@ public static class SiteCommandDtoMapper
             dto.OriginalRaiseTime = Ts(alarm.OriginalRaiseTime.Value);
         }
 
+        if (alarm.AckTime.HasValue)
+        {
+            dto.AckTime = Ts(alarm.AckTime.Value);
+        }
+
         return dto;
     }
 
@@ -1985,7 +1990,8 @@ public static class SiteCommandDtoMapper
             LimitValue = dto.LimitValue,
             NativeSourceCanonicalName = dto.NativeSourceCanonicalName,
             IsConfiguredPlaceholder = dto.IsConfiguredPlaceholder,
-            IsMesReportable = dto.IsMesReportable
+            IsMesReportable = dto.IsMesReportable,
+            AckTime = DtoOrNull(dto.AckTime)
         };
 
         return dto.Condition is null ? alarm : alarm with { Condition = FromProto(dto.Condition) };