feat(dcl): populate obtainable NativeAlarmTransition fields from OPC UA and MxGateway (#27, M2.13)

OPC UA (RealOpcUaClient):
- Append 5 new SelectClauses at indices 13–17 (never renumber 0–12):
  - 13: AlarmConditionType/ActiveState/TransitionTime → OriginalRaiseTime
  - 14–17: LimitAlarmType HighHighLimit/HighLimit/LowLimit/LowLowLimit → LimitValue
- New OpcUaAlarmMapper.PickLimitValue helper: first non-null in HiHi→Hi→Lo→LoLo
  priority order, InvariantCulture-formatted; empty string for non-limit alarm types.
- HandleAlarmEvent reads new indices with fields.Count > N guards; hard minimum (6)
  unchanged so base ConditionType events still process without the limit fields.
- Document unavailable-by-protocol fields (Category, Description, OperatorUser,
  CurrentValue) inline in BuildAlarmEventFilter and HandleAlarmEvent.

MxGateway (MxGatewayAlarmMapper):
- MapTransition: CurrentValue and LimitValue now populated via MxValueToString
  (uses MxValueExtensions.ToClrValue + InvariantCulture) from OnAlarmTransitionEvent
  proto fields current_value/limit_value.
- MapSnapshot: same — populated from ActiveAlarmSnapshot.current_value/limit_value.
- MxValueToString helper (internal): null-safe MxValue → string conversion.

Tests (17 new, 40 total pass):
- OpcUaAlarmMapperTests: PickLimitValue priority, InvariantCulture, all-null case.
- MxGatewayAlarmMapperTests: CurrentValue/LimitValue populate from double/string
  MxValue; absent fields yield empty strings.
- RealOpcUaClientAlarmFilterTests: index alignment assertions (count=18, per-index
  TypeDefinitionId+BrowsePath), regression guard on existing indices 0–12.

src/ZB.MOM.WW.ScadaBridge.DataConnectionLayer/Adapters/RealOpcUaClient.cs

@@ -393,6 +393,34 @@ public class RealOpcUaClient : IOpcUaClient
         filter.SelectClauses.Add(SelectField(ObjectTypeIds.ConditionType, "ConditionName"));                     // 11
         filter.SelectClauses.Add(SelectField(ObjectTypeIds.ConditionType, "Comment"));                           // 12
 
+        // APPENDED fields (indices 13+): optional — only present on specific derived types.
+        // Guard all reads with fields.Count > N so base-ConditionType events still process.
+
+        // 13: AlarmConditionType/ActiveState/TransitionTime — the UTC instant the active-state
+        //     last flipped to TRUE.  Mapped to OriginalRaiseTime; absent on non-AlarmCondition
+        //     events (ConditionType base events rarely carry it).
+        filter.SelectClauses.Add(SelectField(ObjectTypeIds.AlarmConditionType, "ActiveState", "TransitionTime")); // 13
+
+        // 14–17: LimitAlarmType limit thresholds — configuration-time set-points exposed as
+        //        event fields by LimitAlarmType and all its subtypes (Exclusive/NonExclusive
+        //        Level/Deviation/RateOfChange).  Absent on non-limit alarm types (e.g. discrete,
+        //        off-normal) — guarded by fields.Count > N below.
+        filter.SelectClauses.Add(SelectField(ObjectTypeIds.LimitAlarmType, "HighHighLimit"));  // 14
+        filter.SelectClauses.Add(SelectField(ObjectTypeIds.LimitAlarmType, "HighLimit"));      // 15
+        filter.SelectClauses.Add(SelectField(ObjectTypeIds.LimitAlarmType, "LowLimit"));       // 16
+        filter.SelectClauses.Add(SelectField(ObjectTypeIds.LimitAlarmType, "LowLowLimit"));    // 17
+
+        // UNAVAILABLE via standard OPC UA A&C event fields (documented here so future
+        // maintainers know these were considered, not overlooked):
+        //   Category     — not a standard event field; server-specific extensions only.
+        //   Description  — not a per-event text field; the OPC UA Description attribute is a
+        //                  static node property, not carried in event notifications.
+        //   OperatorUser — not available on the standard ConditionRefresh replay stream;
+        //                  present on Acknowledge/Confirm method call results, but those do
+        //                  not flow through the monitored-item subscription.
+        //   CurrentValue — the live process variable value is NOT a standard A&C event field;
+        //                  it would require a separate data subscription on the source node.
+
         ApplyServerSideTypeWhereClause(filter, conditionFilter);
         return filter;
     }
@@ -507,6 +535,23 @@ public class RealOpcUaClient : IOpcUaClient
         var shelve = OpcUaAlarmMapper.MapShelve(fields.Count > 10 ? (fields[10].Value as LocalizedText)?.Text : null);
         var comment = fields.Count > 12 ? (fields[12].Value as LocalizedText)?.Text ?? "" : "";
 
+        // Index 13: ActiveState/TransitionTime → OriginalRaiseTime (when active-state last
+        // transitioned to TRUE).  Absent on non-AlarmCondition events → guard + null fallback.
+        DateTimeOffset? originalRaiseTime = null;
+        if (fields.Count > 13 && fields[13].Value is DateTime activeTransitionTime)
+            originalRaiseTime = new DateTimeOffset(activeTransitionTime, TimeSpan.Zero);
+
+        // Indices 14–17: LimitAlarmType set-point thresholds (HighHighLimit/HighLimit/
+        // LowLimit/LowLowLimit).  Absent on non-limit alarm types → null when missing.
+        // Pick the first non-null value in priority order (HiHi > Hi > Lo > LoLo) as a
+        // display-only representative limit; the caller is responsible for interpreting
+        // which limit is active using AlarmTypeName or ConditionName.
+        var limitValue = OpcUaAlarmMapper.PickLimitValue(
+            fields.Count > 14 ? fields[14].Value : null,
+            fields.Count > 15 ? fields[15].Value : null,
+            fields.Count > 16 ? fields[16].Value : null,
+            fields.Count > 17 ? fields[17].Value : null);
+
         var inRefresh = _alarmInRefresh.GetValueOrDefault(handle);
         var lastState = _alarmLastState.GetValueOrDefault(handle);
         var (prevActive, prevAcked) = lastState != null && lastState.TryGetValue(sourceRef, out var prev) ? prev : (false, true);
@@ -524,15 +569,18 @@ public class RealOpcUaClient : IOpcUaClient
             AlarmTypeName: ResolveAlarmTypeName(eventType),
             Kind: kind,
             Condition: OpcUaAlarmMapper.BuildCondition(active, acked, confirmed, shelve, suppressed, severity),
+            // UNAVAILABLE via standard OPC UA A&C event fields — see BuildAlarmEventFilter comments.
             Category: "",
             Description: "",
             Message: message,
+            // UNAVAILABLE: OperatorUser not on refresh stream — see BuildAlarmEventFilter comments.
             OperatorUser: "",
             OperatorComment: comment,
-            OriginalRaiseTime: null,
+            OriginalRaiseTime: originalRaiseTime,
             TransitionTime: time,
+            // UNAVAILABLE: CurrentValue not a standard A&C event field — see BuildAlarmEventFilter.
             CurrentValue: "",
-            LimitValue: ""));
+            LimitValue: limitValue));
     }
 
     private static NativeAlarmTransition SnapshotComplete() => new(