feat(triggers): add WhileTrue fire mode for Conditional/Expression script triggers

Conditional and Expression script triggers gain an optional `mode` field
in their TriggerConfiguration JSON:

- OnTrue (default): unchanged edge/per-change firing. An absent mode field
  parses as OnTrue, so every existing trigger config behaves identically.
- WhileTrue: fires on the false->true edge, then re-fires on a periodic
  timer while the condition holds; stops on the true->false edge. The
  re-fire cadence is the script's MinTimeBetweenRuns; with none configured
  the trigger degrades to a single edge fire and logs a warning.

ScriptActor tracks condition truth state and manages a dedicated
"whiletrue-trigger" timer. ScriptTriggerConfigCodec and ScriptTriggerEditor
round-trip the mode and expose an OnTrue/WhileTrue selector for the two
trigger kinds. Design: docs/plans/2026-05-18-whiletrue-trigger-mode-design.md

Tests: 7 ScriptActor runtime tests (edge fire, timer re-fire, stop,
re-arm, no-MinTimeBetweenRuns degrade, OnTrue regressions) + 14 codec /
editor tests. SiteRuntime suite 206 green, CentralUI suite 295 green.

tests/ScadaLink.CentralUI.Tests/Shared/ScriptTriggerEditorTests.cs

@@ -0,0 +1,69 @@
+using Bunit;
+using Microsoft.AspNetCore.Components;
+using ScadaLink.CentralUI.Components.Shared;
+
+namespace ScadaLink.CentralUI.Tests.Shared;
+
+/// <summary>
+/// Component tests for the OnTrue/WhileTrue mode selector that
+/// <see cref="ScriptTriggerEditor"/> exposes for Conditional and Expression
+/// triggers.
+/// </summary>
+public class ScriptTriggerEditorTests : BunitContext
+{
+    private const string ConditionalConfig =
+        @"{""attributeName"":""Temp"",""operator"":"">"",""threshold"":50}";
+
+    private const string ConditionalWhileTrueConfig =
+        @"{""attributeName"":""Temp"",""operator"":"">"",""threshold"":50,""mode"":""WhileTrue""}";
+
+    [Fact]
+    public void SelectingWhileTrue_EmitsConfigWithWhileTrueMode()
+    {
+        ScriptTriggerValue? captured = null;
+        var cut = Render<ScriptTriggerEditor>(ps => ps
+            .Add(p => p.TriggerType, "Conditional")
+            .Add(p => p.TriggerConfig, ConditionalConfig)
+            .Add(p => p.Changed,
+                EventCallback.Factory.Create<ScriptTriggerValue>(this, v => captured = v)));
+
+        cut.Find("#script-trigger-mode").Change("WhileTrue");
+
+        Assert.NotNull(captured);
+        Assert.Contains("\"mode\":\"WhileTrue\"", captured!.Config);
+    }
+
+    [Fact]
+    public void ModeSelector_DefaultsToOnTrue_WhenConfigHasNoMode()
+    {
+        ScriptTriggerValue? captured = null;
+        var cut = Render<ScriptTriggerEditor>(ps => ps
+            .Add(p => p.TriggerType, "Conditional")
+            .Add(p => p.TriggerConfig, ConditionalConfig)
+            .Add(p => p.Changed,
+                EventCallback.Factory.Create<ScriptTriggerValue>(this, v => captured = v)));
+
+        // Change the threshold to force an emit without touching the mode.
+        cut.Find("input[type=number]").Input("75");
+
+        Assert.NotNull(captured);
+        Assert.Contains("\"mode\":\"OnTrue\"", captured!.Config);
+    }
+
+    [Fact]
+    public void LoadedWhileTrueMode_IsRetainedAcrossAnUnrelatedEdit()
+    {
+        ScriptTriggerValue? captured = null;
+        var cut = Render<ScriptTriggerEditor>(ps => ps
+            .Add(p => p.TriggerType, "Conditional")
+            .Add(p => p.TriggerConfig, ConditionalWhileTrueConfig)
+            .Add(p => p.Changed,
+                EventCallback.Factory.Create<ScriptTriggerValue>(this, v => captured = v)));
+
+        // Editing the threshold must not silently drop the loaded WhileTrue mode.
+        cut.Find("input[type=number]").Input("75");
+
+        Assert.NotNull(captured);
+        Assert.Contains("\"mode\":\"WhileTrue\"", captured!.Config);
+    }
+}