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.Commons/Types/Enums/AlarmLevel.cs

@@ -0,0 +1,19 @@
+namespace ScadaLink.Commons.Types.Enums;
+
+/// <summary>
+/// Severity level for an active alarm. Binary alarm types (ValueMatch,
+/// RangeViolation, RateOfChange) always emit <see cref="None"/>. The HiLo
+/// trigger type emits one of the directional levels based on which setpoint
+/// the monitored attribute has crossed.
+///
+/// Conventional ordering (lowest setpoint to highest):
+///   LowLow &lt; Low &lt; normal-band &lt; High &lt; HighHigh
+/// </summary>
+public enum AlarmLevel
+{
+    None,
+    Low,
+    LowLow,
+    High,
+    HighHigh
+}

src/ScadaLink.Commons/Types/Enums/AlarmTriggerType.cs

@@ -4,5 +4,12 @@ public enum AlarmTriggerType
 {
     ValueMatch,
     RangeViolation,
-    RateOfChange
+    RateOfChange,
+    /// <summary>
+    /// Multi-setpoint level alarm: monitors a single numeric attribute against
+    /// up to four configurable setpoints (LoLo, Lo, Hi, HiHi). Each setpoint
+    /// may carry its own priority; transitions between levels emit a fresh
+    /// AlarmStateChanged with the corresponding <see cref="AlarmLevel"/>.
+    /// </summary>
+    HiLo
 }

src/ScadaLink.Commons/Types/Scripts/AlarmContext.cs

@@ -0,0 +1,23 @@
+using ScadaLink.Commons.Types.Enums;
+
+namespace ScadaLink.Commons.Types.Scripts;
+
+/// <summary>
+/// Alarm context exposed to on-trigger scripts via <c>Alarm</c>. Lets scripts
+/// branch on the firing severity — e.g., page on-call for HiHi/LoLo but only
+/// email the day shift for Hi/Lo. Always present when an on-trigger script
+/// runs; <see cref="Level"/> is <see cref="AlarmLevel.None"/> for binary
+/// trigger types.
+/// </summary>
+public sealed class AlarmContext
+{
+    public string Name { get; init; } = string.Empty;
+    public AlarmLevel Level { get; init; } = AlarmLevel.None;
+    public int Priority { get; init; }
+
+    /// <summary>
+    /// Per-band operator message configured on the HiLo alarm, or empty for
+    /// binary trigger types and bands without a message.
+    /// </summary>
+    public string Message { get; init; } = string.Empty;
+}