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/Messages/Management/InstanceCommands.cs

@@ -10,3 +10,21 @@ public record MgmtDeleteInstanceCommand(int InstanceId);
 public record SetConnectionBindingsCommand(int InstanceId, IReadOnlyList<(string AttributeName, int DataConnectionId)> Bindings);
 public record SetInstanceOverridesCommand(int InstanceId, IReadOnlyDictionary<string, string?> Overrides);
 public record SetInstanceAreaCommand(int InstanceId, int? AreaId);
+
+/// <summary>
+/// Sets (or upserts) a per-instance alarm override. For HiLo trigger types the
+/// <c>TriggerConfigurationOverride</c> JSON is merged setpoint-by-setpoint with
+/// the inherited config; for binary trigger types it replaces the whole config.
+/// Either field is optional — pass null to leave it unchanged.
+/// </summary>
+public record SetInstanceAlarmOverrideCommand(
+    int InstanceId,
+    string AlarmCanonicalName,
+    string? TriggerConfigurationOverride,
+    int? PriorityLevelOverride);
+
+public record DeleteInstanceAlarmOverrideCommand(
+    int InstanceId,
+    string AlarmCanonicalName);
+
+public record ListInstanceAlarmOverridesCommand(int InstanceId);