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

tests/ZB.MOM.WW.ScadaBridge.Communication.Tests/Grpc/SiteStreamGrpcClientTests.cs

@@ -96,7 +96,8 @@ public class SiteStreamGrpcClientTests
         Assert.False(alarm.Condition.Acknowledged);
         Assert.Equal(AlarmShelveState.TimedShelved, alarm.Condition.Shelve);
         Assert.True(alarm.Condition.Suppressed);
-        Assert.Equal(850, alarm.Condition.Severity);
+        Assert.Equal(850, alarm.Condition.Severity);   // OPC UA: wire value is Part 9 Severity already
+        Assert.Equal(850, alarm.Condition.Priority);
         Assert.Equal("T01.Hi", alarm.SourceReference);
         Assert.Equal("AnalogLimit.Hi", alarm.AlarmTypeName);
         Assert.Equal("Process", alarm.Category);
@@ -107,6 +108,41 @@ public class SiteStreamGrpcClientTests
         Assert.Equal("100", alarm.LimitValue);
     }
 
+    /// <summary>
+    /// Gitea #129: the wire carries the raw priority. MxAccess and computed rows band it onto a
+    /// higher-is-more-urgent Severity (AVEVA priority 1 → 1000); the raw value stays on Priority.
+    /// The wire meaning is unchanged, so this is also right for a site on an older build.
+    /// </summary>
+    [Theory]
+    [InlineData("NativeMxAccess", 1, 1000)]
+    [InlineData("NativeMxAccess", 400, 750)]
+    [InlineData("NativeMxAccess", 950, 250)]
+    [InlineData("Computed", 100, 1000)]
+    [InlineData("Computed", 700, 500)]
+    [InlineData("NativeOpcUa", 950, 950)]
+    public void ConvertToDomainEvent_AlarmChanged_SeverityIsOneDirection(string kind, int wirePriority, int expectedSeverity)
+    {
+        var evt = new SiteStreamEvent
+        {
+            AlarmChanged = new AlarmStateUpdate
+            {
+                InstanceUniqueName = "Site1.Motor01",
+                AlarmName = "A",
+                State = AlarmStateEnum.AlarmStateActive,
+                Priority = wirePriority,
+                Timestamp = Timestamp.FromDateTimeOffset(DateTimeOffset.UnixEpoch),
+                Kind = kind,
+                Active = true
+            }
+        };
+
+        var alarm = Assert.IsType<AlarmStateChanged>(SiteStreamGrpcClient.ConvertToDomainEvent(evt));
+
+        Assert.Equal(expectedSeverity, alarm.Condition.Severity);
+        Assert.Equal(wirePriority, alarm.Condition.Priority);
+        Assert.Equal(wirePriority, alarm.Priority);
+    }
+
     /// <summary>Verifies that an unknown stream event converts to null.</summary>
     [Fact]
     public void ConvertToDomainEvent_UnknownEvent_ReturnsNull()