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

tests/ZB.MOM.WW.ScadaBridge.Communication.Tests/SiteCommandSamples.cs

@@ -290,7 +290,11 @@ internal static class SiteCommandSamples
             IsMesReportable = true
         };
 
-    /// <summary>A mirrored native alarm: every native enrichment field populated, <c>Condition</c> explicit.</summary>
+    /// <summary>
+    /// A mirrored native alarm: every native enrichment field populated, <c>Condition</c> explicit.
+    /// Carries an ack time so the golden pins <c>DebugAlarmStateDto</c> field 21 (Gitea #84); the
+    /// computed sample leaves it null, pinning the absent-means-null decode.
+    /// </summary>
     private static AlarmStateChanged NativeAlarm() =>
         new("Site1.Pump1", "Tank01.Level.HiHi", AlarmState.Active, 850, T2)
         {
@@ -304,6 +308,7 @@ internal static class SiteCommandSamples
             OperatorUser = "multi-role",
             OperatorComment = "ack'd at panel",
             OriginalRaiseTime = T1,
+            AckTime = T2,
             CurrentValue = "91.2",
             LimitValue = "90.0",
             NativeSourceCanonicalName = "Tank01.TankAlarms",