feat(alarms): HiLo trigger type with per-band level, hysteresis, messages, overrides

Adds a new HiLo alarm trigger type with four configurable setpoints
(LoLo / Lo / Hi / HiHi). Each setpoint carries an optional priority,
deadband (for hysteresis), and operator message. The site runtime emits
AlarmStateChanged with an AlarmLevel field so consumers can differentiate
warning vs critical bands.

Plumbing:
  - new AlarmLevel enum + AlarmStateChanged.Level/Message init properties
  - AlarmTriggerEditor (Blazor) gets a HiLo render with severity tinting
  - AlarmTriggerConfigCodec extracted from the editor for testability
  - sitestream.proto carries level + message over gRPC
  - SemanticValidator enforces numeric attribute, setpoint ordering,
    non-negative deadband
  - on-trigger scripts get an Alarm global (Name/Level/Priority/Message)
    so notification routing can branch by severity
  - per-instance InstanceAlarmOverride entity + EF migration + flattening
    step + CLI commands; HiLo overrides merge setpoint-by-setpoint, binary
    types whole-replace
  - DebugView shows a Level badge + per-band message tooltip
  - App.razor auto-reloads on permanent Blazor circuit failure
  - docker/regen-proto.sh automates the proto regen workflow (the linux/arm64
    protoc segfault means generated files are checked in for now)

src/ScadaLink.Communication/Grpc/SiteStreamGrpcClient.cs

@@ -137,7 +137,11 @@ public class SiteStreamGrpcClient : IAsyncDisposable
             evt.AlarmChanged.AlarmName,
             MapAlarmState(evt.AlarmChanged.State),
             evt.AlarmChanged.Priority,
-            evt.AlarmChanged.Timestamp.ToDateTimeOffset()),
+            evt.AlarmChanged.Timestamp.ToDateTimeOffset())
+        {
+            Level = MapAlarmLevel(evt.AlarmChanged.Level),
+            Message = evt.AlarmChanged.Message ?? string.Empty
+        },
         _ => null
     };
 
@@ -162,6 +166,18 @@ public class SiteStreamGrpcClient : IAsyncDisposable
         _ => AlarmState.Normal
     };
 
+    /// <summary>
+    /// Maps proto AlarmLevelEnum to domain AlarmLevel. Internal for testability.
+    /// </summary>
+    internal static AlarmLevel MapAlarmLevel(AlarmLevelEnum level) => level switch
+    {
+        AlarmLevelEnum.AlarmLevelLow => AlarmLevel.Low,
+        AlarmLevelEnum.AlarmLevelLowLow => AlarmLevel.LowLow,
+        AlarmLevelEnum.AlarmLevelHigh => AlarmLevel.High,
+        AlarmLevelEnum.AlarmLevelHighHigh => AlarmLevel.HighHigh,
+        _ => AlarmLevel.None
+    };
+
     public async ValueTask DisposeAsync()
     {
         foreach (var cts in _subscriptions.Values)