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.ConfigurationDatabase/Configurations/InstanceConfiguration.cs

@@ -41,6 +41,11 @@ public class InstanceConfiguration : IEntityTypeConfiguration<Instance>
             .HasForeignKey(o => o.InstanceId)
             .OnDelete(DeleteBehavior.Cascade);
 
+        builder.HasMany(i => i.AlarmOverrides)
+            .WithOne()
+            .HasForeignKey(o => o.InstanceId)
+            .OnDelete(DeleteBehavior.Cascade);
+
         builder.HasMany(i => i.ConnectionBindings)
             .WithOne()
             .HasForeignKey(b => b.InstanceId)
@@ -67,6 +72,23 @@ public class InstanceAttributeOverrideConfiguration : IEntityTypeConfiguration<I
     }
 }
 
+public class InstanceAlarmOverrideConfiguration : IEntityTypeConfiguration<InstanceAlarmOverride>
+{
+    public void Configure(EntityTypeBuilder<InstanceAlarmOverride> builder)
+    {
+        builder.HasKey(o => o.Id);
+
+        builder.Property(o => o.AlarmCanonicalName)
+            .IsRequired()
+            .HasMaxLength(400); // Larger than attribute names to fit composed paths.
+
+        builder.Property(o => o.TriggerConfigurationOverride)
+            .HasMaxLength(4000);
+
+        builder.HasIndex(o => new { o.InstanceId, o.AlarmCanonicalName }).IsUnique();
+    }
+}
+
 public class InstanceConnectionBindingConfiguration : IEntityTypeConfiguration<InstanceConnectionBinding>
 {
     public void Configure(EntityTypeBuilder<InstanceConnectionBinding> builder)