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

docker/seed-mes-test-machine.sh

@@ -302,6 +302,10 @@ CS
 # The MES alarm-status projection (same as docker/seed-mes-alarm-demo.sh). Computed alarms report
 # Acknowledged=true / AckTime=null by construction, so StatusCode reads "Triggered.Acked" and
 # IncludeAcked=false drops every computed alarm (it only bites on mirrored native conditions).
+# MES `Severity` / `MinSeverity` / `MaxSeverity` are the raw 0-999 priority, read from
+# `ScriptAlarm.Priority` — NOT `ScriptAlarm.Severity`, which since Gitea #129 is the banded,
+# higher-is-more-urgent severity (priority 1-250 -> 1000 ... 751-999 -> 250). Priority keeps the
+# value Severity carried before #129, so MES sees exactly the same numbers and filters as before.
 read -r -d '' ALARM_CODE <<'CS' || true
 var code        = Parameters["MachineCode"]?.ToString() ?? "";
 var flaggedOnly = Parameters.Get<bool?>("FlaggedOnly") ?? false;
@@ -313,8 +317,8 @@ try {
     var alarms = flaggedOnly ? await Alarms.MesReportableAsync() : await Alarms.CurrentAsync();
     var infos = alarms
         .Where(a => a.Active && !a.IsConfiguredPlaceholder)
-        .Where(a => minSev == null || a.Severity >= minSev)
-        .Where(a => maxSev == null || a.Severity <= maxSev)
+        .Where(a => minSev == null || a.Priority >= minSev)
+        .Where(a => maxSev == null || a.Priority <= maxSev)
         .Where(a => string.IsNullOrEmpty(nameFilter) || a.Name.Contains(nameFilter, StringComparison.OrdinalIgnoreCase))
         .Where(a => includeAck || !a.Acknowledged)
         .Select(a => new {
@@ -322,7 +326,7 @@ try {
             HierarchicalName = code + "." + a.Name,
             Description = !string.IsNullOrEmpty(a.Message) ? a.Message : !string.IsNullOrEmpty(a.AlarmTypeName) ? a.AlarmTypeName : a.Name,
             IsFlaggedForMES = a.IsMesReportable,
-            Severity = a.Severity,
+            Severity = a.Priority,   // MES Severity = the raw 0-999 priority (ScriptAlarm.Priority, #129)
             StatusCode = a.Acknowledged ? "Triggered.Acked" : "Triggered",
             TriggeredDT = (a.OriginalRaiseTime ?? a.Timestamp).ToString("o"),
             AckDT = a.AckTime?.ToString("o"),