feat(ui/triggers): expression trigger panel in the script & alarm editors

src/ScadaLink.CentralUI/Components/Shared/AlarmTriggerEditor.razor

@@ -12,6 +12,10 @@
 <div class="border rounded bg-white p-3">
 
     @* ── Monitored attribute ───────────────────────────────────────────── *@
+    @* Expression triggers reference attributes inside the C# expression itself,
+       so they do not use the single-attribute picker. *@
+    @if (TriggerType != AlarmTriggerType.Expression)
+    {
     <div class="mb-3">
         <label for="alarm-attr-select" class="form-label small text-uppercase text-muted fw-semibold mb-1">
             Monitored attribute
@@ -67,6 +71,7 @@
             </div>
         }
     </div>
+    }
 
     @* ── Type-specific block ───────────────────────────────────────────── *@
     @switch (TriggerType)
@@ -83,6 +88,9 @@
         case AlarmTriggerType.HiLo:
             @RenderHiLo();
             break;
+        case AlarmTriggerType.Expression:
+            @RenderExpression();
+            break;
     }
 
     @* ── Hint ──────────────────────────────────────────────────────────── *@
@@ -559,6 +567,30 @@
         await Emit();
     }
 
+    // ── Expression ─────────────────────────────────────────────────────────
+
+    private RenderFragment RenderExpression() => __builder =>
+    {
+        <label class="form-label small text-uppercase text-muted fw-semibold mb-1">Trigger expression</label>
+        <MonacoEditor Height="120px"
+                      Language="csharp"
+                      ScriptKind="ScriptAnalysis.ScriptKind.Template"
+                      ShowToolbar="false"
+                      Value="@(_model.Expression ?? string.Empty)"
+                      ValueChanged="OnExpressionChanged"
+                      SelfAttributes="@TriggerAttributeMapper.SelfAttributes(AvailableAttributes)"
+                      Children="@TriggerAttributeMapper.Children(AvailableAttributes)" />
+        <div class="form-text">
+            A boolean C# expression — e.g. <code>Attributes["Temperature"] &gt; 80</code>.
+        </div>
+    };
+
+    private async Task OnExpressionChanged(string value)
+    {
+        _model.Expression = value;
+        await Emit();
+    }
+
     // ── Hint text ──────────────────────────────────────────────────────────
 
     private string BuildHint()
@@ -582,6 +614,9 @@
 
             AlarmTriggerType.HiLo => BuildHiLoHint(attr),
 
+            AlarmTriggerType.Expression =>
+                "Alarm is active while this expression is true.",
+
             _ => string.Empty
         };
     }