fix(triggers): use explicit ValidationCategory + tighten expression syntax validation

src/ScadaLink.TemplateEngine/Validation/ScriptCompiler.cs

@@ -12,8 +12,13 @@ namespace ScadaLink.TemplateEngine.Validation;
 /// </summary>
 public class ScriptCompiler
 {
-    // Forbidden namespace patterns - scripts must not use these
-    private static readonly string[] ForbiddenPatterns =
+    /// <summary>
+    /// Forbidden namespace patterns — scripts (and trigger expressions, via
+    /// <see cref="ValidationService"/>) must not use these. Trigger expressions run
+    /// under the same trust model as scripts, so the list is shared from here rather
+    /// than duplicated.
+    /// </summary>
+    internal static readonly string[] ForbiddenPatterns =
     [
         "System.IO.",
         "System.Diagnostics.Process",