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/Migrations/20260513055537_AddInstanceAlarmOverrides.cs

@@ -0,0 +1,49 @@
+using Microsoft.EntityFrameworkCore.Migrations;
+
+#nullable disable
+
+namespace ScadaLink.ConfigurationDatabase.Migrations
+{
+    /// <inheritdoc />
+    public partial class AddInstanceAlarmOverrides : Migration
+    {
+        /// <inheritdoc />
+        protected override void Up(MigrationBuilder migrationBuilder)
+        {
+            migrationBuilder.CreateTable(
+                name: "InstanceAlarmOverrides",
+                columns: table => new
+                {
+                    Id = table.Column<int>(type: "int", nullable: false)
+                        .Annotation("SqlServer:Identity", "1, 1"),
+                    InstanceId = table.Column<int>(type: "int", nullable: false),
+                    AlarmCanonicalName = table.Column<string>(type: "nvarchar(400)", maxLength: 400, nullable: false),
+                    TriggerConfigurationOverride = table.Column<string>(type: "nvarchar(4000)", maxLength: 4000, nullable: true),
+                    PriorityLevelOverride = table.Column<int>(type: "int", nullable: true)
+                },
+                constraints: table =>
+                {
+                    table.PrimaryKey("PK_InstanceAlarmOverrides", x => x.Id);
+                    table.ForeignKey(
+                        name: "FK_InstanceAlarmOverrides_Instances_InstanceId",
+                        column: x => x.InstanceId,
+                        principalTable: "Instances",
+                        principalColumn: "Id",
+                        onDelete: ReferentialAction.Cascade);
+                });
+
+            migrationBuilder.CreateIndex(
+                name: "IX_InstanceAlarmOverrides_InstanceId_AlarmCanonicalName",
+                table: "InstanceAlarmOverrides",
+                columns: new[] { "InstanceId", "AlarmCanonicalName" },
+                unique: true);
+        }
+
+        /// <inheritdoc />
+        protected override void Down(MigrationBuilder migrationBuilder)
+        {
+            migrationBuilder.DropTable(
+                name: "InstanceAlarmOverrides");
+        }
+    }
+}

src/ScadaLink.ConfigurationDatabase/Migrations/ScadaLinkDbContextModelSnapshot.cs

@@ -478,6 +478,37 @@ namespace ScadaLink.ConfigurationDatabase.Migrations
                     b.ToTable("Instances");
                 });
 
+            modelBuilder.Entity("ScadaLink.Commons.Entities.Instances.InstanceAlarmOverride", b =>
+                {
+                    b.Property<int>("Id")
+                        .ValueGeneratedOnAdd()
+                        .HasColumnType("int");
+
+                    SqlServerPropertyBuilderExtensions.UseIdentityColumn(b.Property<int>("Id"));
+
+                    b.Property<string>("AlarmCanonicalName")
+                        .IsRequired()
+                        .HasMaxLength(400)
+                        .HasColumnType("nvarchar(400)");
+
+                    b.Property<int>("InstanceId")
+                        .HasColumnType("int");
+
+                    b.Property<int?>("PriorityLevelOverride")
+                        .HasColumnType("int");
+
+                    b.Property<string>("TriggerConfigurationOverride")
+                        .HasMaxLength(4000)
+                        .HasColumnType("nvarchar(4000)");
+
+                    b.HasKey("Id");
+
+                    b.HasIndex("InstanceId", "AlarmCanonicalName")
+                        .IsUnique();
+
+                    b.ToTable("InstanceAlarmOverrides");
+                });
+
             modelBuilder.Entity("ScadaLink.Commons.Entities.Instances.InstanceAttributeOverride", b =>
                 {
                     b.Property<int>("Id")
@@ -1144,6 +1175,15 @@ namespace ScadaLink.ConfigurationDatabase.Migrations
                         .IsRequired();
                 });
 
+            modelBuilder.Entity("ScadaLink.Commons.Entities.Instances.InstanceAlarmOverride", b =>
+                {
+                    b.HasOne("ScadaLink.Commons.Entities.Instances.Instance", null)
+                        .WithMany("AlarmOverrides")
+                        .HasForeignKey("InstanceId")
+                        .OnDelete(DeleteBehavior.Cascade)
+                        .IsRequired();
+                });
+
             modelBuilder.Entity("ScadaLink.Commons.Entities.Instances.InstanceAttributeOverride", b =>
                 {
                     b.HasOne("ScadaLink.Commons.Entities.Instances.Instance", null)
@@ -1271,6 +1311,8 @@ namespace ScadaLink.ConfigurationDatabase.Migrations
 
             modelBuilder.Entity("ScadaLink.Commons.Entities.Instances.Instance", b =>
                 {
+                    b.Navigation("AlarmOverrides");
+
                     b.Navigation("AttributeOverrides");
 
                     b.Navigation("ConnectionBindings");