feat(runtime): ScriptedAlarmActor state machine (engine wiring tracked as F9)

src/Server/ZB.MOM.WW.OtOpcUa.Runtime/ScriptedAlarms/ScriptedAlarmActor.cs

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+using Akka.Actor;
+using Akka.Event;
+
+namespace ZB.MOM.WW.OtOpcUa.Runtime.ScriptedAlarms;
+
+public enum ScriptedAlarmActorState { Inactive, Active, Acknowledged }
+
+/// <summary>
+/// State machine wrapping a single scripted alarm. Transitions:
+/// <c>Inactive → Active → Acknowledged → Inactive</c>.
+///
+/// Engine wiring (compile alarm expression via <c>AlarmConditionService</c>, persist state to
+/// <c>ScriptedAlarmState</c> ConfigDb table on <c>PreRestart</c>, emit history rows to
+/// <c>HistorianAdapter</c>) is staged for follow-up F9. This skeleton owns the state machine
+/// so DriverHostActor can spawn it as a child.
+/// </summary>
+public sealed class ScriptedAlarmActor : ReceiveActor
+{
+    public sealed record ConditionMet(string Reason);
+    public sealed record AcknowledgeAlarm(string Actor);
+    public sealed record ConditionCleared;
+    public sealed record StateChanged(string AlarmId, ScriptedAlarmActorState State, DateTime AtUtc);
+
+    private readonly string _alarmId;
+    private readonly ILoggingAdapter _log = Context.GetLogger();
+    private ScriptedAlarmActorState _state = ScriptedAlarmActorState.Inactive;
+
+    public static Props Props(string alarmId) =>
+        Akka.Actor.Props.Create(() => new ScriptedAlarmActor(alarmId));
+
+    public ScriptedAlarmActor(string alarmId)
+    {
+        _alarmId = alarmId;
+
+        Receive<ConditionMet>(msg =>
+        {
+            if (_state != ScriptedAlarmActorState.Inactive) return;
+            Transition(ScriptedAlarmActorState.Active);
+        });
+        Receive<AcknowledgeAlarm>(msg =>
+        {
+            if (_state != ScriptedAlarmActorState.Active) return;
+            Transition(ScriptedAlarmActorState.Acknowledged);
+        });
+        Receive<ConditionCleared>(_ =>
+        {
+            if (_state == ScriptedAlarmActorState.Inactive) return;
+            Transition(ScriptedAlarmActorState.Inactive);
+        });
+    }
+
+    private void Transition(ScriptedAlarmActorState next)
+    {
+        var prev = _state;
+        _state = next;
+        _log.Info("ScriptedAlarm {Id}: {From} → {To}", _alarmId, prev, next);
+        Context.Parent.Tell(new StateChanged(_alarmId, next, DateTime.UtcNow));
+        // F9: emit history row via HistorianAdapter; persist state to ScriptedAlarmState DB.
+    }
+}