fix(alarms): Severity runs one direction, higher = more urgent; raw priority kept (#129)

AlarmConditionState.Severity mixed two conventions: OPC UA rows carried Part 9
Severity (higher = more severe) while MxGateway native alarms and computed
alarms carried a raw AVEVA-style priority (1 = most urgent). Every consumer
ranks higher as worse, so Worst Severity, the severity filter/sort and the
site event-log Error threshold picked the LEAST urgent MxGateway/computed
alarms.

- AlarmPriorityBands: the OtOpcUa GalaxyAlarmPriority table (lmxopcua#887,
  b61f3e05), value for value: 1-250 -> 1000, 251-500 -> 750, 501-750 -> 500,
  751-999 -> 250; <= 0 clamps to Critical, > 999 to Low.
- MxGatewayAlarmMapper bands the gateway severity (= AVEVA priority);
  AlarmConditionStateFactory.ForComputed bands PriorityLevel. OPC UA unchanged.
- AlarmConditionState gains trailing Priority (int?): the raw source number,
  exactly the pre-#129 Severity. AlarmStateChanged.Priority and the wire
  AlarmStateUpdate.priority keep that meaning (no proto change); central derives
  Severity by kind (SeverityFromPriority), so an older site decodes correctly.
- ScriptAlarm gains trailing Priority. The native MES 900-999 band and the MES
  API Severity/MinSeverity/MaxSeverity key off Priority; rig seed scripts moved
  from a.Severity to a.Priority, so MES output is unchanged.
- AlarmActor raise logs Error when the banded severity >= 700 (same threshold
  as NativeAlarmActor): priority 1-500 Error, 501+ Warning (was raw >= 700).
- NativeAlarmActor upgrades pre-#129 native_alarm_state rows on rehydrate.
- Debug snapshot decode restores Condition.Priority from the row's priority.
- Docs: Commons, DCL, SiteRuntime, Communication, CentralUI, InboundAPI,
  HighLevelReqs, MES alarm-status plan, CLAUDE.md.

Claude-Session: https://claude.ai/code/session_01GT67ACmpMR7b9LGRPLijMi

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

@@ -575,43 +575,56 @@ public class SiteStreamGrpcClient : IAsyncDisposable, IDisposable
             // proto3 defaults, which map to null / false.
             SourceExecutionId: Guid.TryParse(evt.AttributeChanged.SourceExecutionId, out var traceSource) ? traceSource : null,
             Trace: evt.AttributeChanged.Trace),
-        SiteStreamEvent.EventOneofCase.AlarmChanged => new AlarmStateChanged(
-            evt.AlarmChanged.InstanceUniqueName,
-            evt.AlarmChanged.AlarmName,
-            MapAlarmState(evt.AlarmChanged.State),
-            evt.AlarmChanged.Priority,
-            evt.AlarmChanged.Timestamp.ToDateTimeOffset())
-        {
-            Level = MapAlarmLevel(evt.AlarmChanged.Level),
-            Message = evt.AlarmChanged.Message ?? string.Empty,
-            // Native alarm enrichment (additive — computed alarms carry their default condition).
-            Kind = ParseAlarmKind(evt.AlarmChanged.Kind),
-            Condition = new AlarmConditionState(
-                Active: evt.AlarmChanged.Active,
-                Acknowledged: evt.AlarmChanged.Acknowledged,
-                Confirmed: evt.AlarmChanged.Confirmed,
-                Shelve: AlarmShelveStateCodec.Parse(evt.AlarmChanged.ShelveState),
-                Suppressed: evt.AlarmChanged.Suppressed,
-                Severity: evt.AlarmChanged.Priority),
-            SourceReference = evt.AlarmChanged.SourceReference ?? string.Empty,
-            AlarmTypeName = evt.AlarmChanged.AlarmTypeName ?? string.Empty,
-            Category = evt.AlarmChanged.Category ?? string.Empty,
-            OperatorUser = evt.AlarmChanged.OperatorUser ?? string.Empty,
-            OperatorComment = evt.AlarmChanged.OperatorComment ?? string.Empty,
-            OriginalRaiseTime = evt.AlarmChanged.OriginalRaiseTime?.ToDateTimeOffset(),
-            CurrentValue = evt.AlarmChanged.CurrentValue ?? string.Empty,
-            LimitValue = evt.AlarmChanged.LimitValue ?? string.Empty,
-            NativeSourceCanonicalName = evt.AlarmChanged.NativeSourceCanonicalName ?? string.Empty,
-            IsConfiguredPlaceholder = evt.AlarmChanged.IsConfiguredPlaceholder,
-            // MES alarm-status API §6.4: ack instant; an absent proto Timestamp (unacked
-            // condition, computed alarm, or a pre-AckTime site) stays null.
-            AckTime = evt.AlarmChanged.AckTime?.ToDateTimeOffset(),
-            // Gitea #60: a pre-#60 site leaves the field at its proto3 default (false).
-            IsMesReportable = evt.AlarmChanged.IsMesReportable
-        },
+        SiteStreamEvent.EventOneofCase.AlarmChanged => ConvertAlarmChanged(evt.AlarmChanged),
         _ => null
     };
 
+    /// <summary>
+    /// Maps one <see cref="AlarmStateUpdate"/> to the domain record. The wire carries only the raw
+    /// <c>priority</c> (its pre-#129 meaning, unchanged), so the unified, higher-is-more-urgent
+    /// Severity is derived here from the kind (Gitea #129): banded for MxAccess and computed rows,
+    /// verbatim for OPC UA. The raw value stays on <see cref="AlarmConditionState.Priority"/>.
+    /// </summary>
+    private static AlarmStateChanged ConvertAlarmChanged(AlarmStateUpdate update)
+    {
+        var kind = ParseAlarmKind(update.Kind);
+        return new AlarmStateChanged(
+            update.InstanceUniqueName,
+            update.AlarmName,
+            MapAlarmState(update.State),
+            update.Priority,
+            update.Timestamp.ToDateTimeOffset())
+        {
+            Level = MapAlarmLevel(update.Level),
+            Message = update.Message ?? string.Empty,
+            // Native alarm enrichment (additive — computed alarms carry their default condition).
+            Kind = kind,
+            Condition = new AlarmConditionState(
+                Active: update.Active,
+                Acknowledged: update.Acknowledged,
+                Confirmed: update.Confirmed,
+                Shelve: AlarmShelveStateCodec.Parse(update.ShelveState),
+                Suppressed: update.Suppressed,
+                Severity: AlarmConditionStateFactory.SeverityFromPriority(kind, update.Priority),
+                Priority: update.Priority),
+            SourceReference = update.SourceReference ?? string.Empty,
+            AlarmTypeName = update.AlarmTypeName ?? string.Empty,
+            Category = update.Category ?? string.Empty,
+            OperatorUser = update.OperatorUser ?? string.Empty,
+            OperatorComment = update.OperatorComment ?? string.Empty,
+            OriginalRaiseTime = update.OriginalRaiseTime?.ToDateTimeOffset(),
+            CurrentValue = update.CurrentValue ?? string.Empty,
+            LimitValue = update.LimitValue ?? string.Empty,
+            NativeSourceCanonicalName = update.NativeSourceCanonicalName ?? string.Empty,
+            IsConfiguredPlaceholder = update.IsConfiguredPlaceholder,
+            // MES alarm-status API §6.4: ack instant; an absent proto Timestamp (unacked
+            // condition, computed alarm, or a pre-AckTime site) stays null.
+            AckTime = update.AckTime?.ToDateTimeOffset(),
+            // Gitea #60: a pre-#60 site leaves the field at its proto3 default (false).
+            IsMesReportable = update.IsMesReportable
+        };
+    }
+
     /// <summary>
     /// Maps a proto <see cref="SiteStreamEvent"/> to a domain <see cref="AlarmStateChanged"/>,
     /// returning <c>null</c> for any non-alarm event. Used by <see cref="SubscribeSiteAsync"/>