feat(runtime): per-script execution timeout overriding the global default (#9)

Spec promised a per-script timeout but only the global ScriptExecutionTimeoutSeconds
existed. Add nullable TemplateScript.ExecutionTimeoutSeconds threaded through EF +
flattening (ResolvedScript) to ScriptExecutionActor/AlarmExecutionActor, which use
perScript ?? global for the execution CTS. Includes the EF migration for the new column.

src/ZB.MOM.WW.ScadaBridge.Transport/Serialization/EntityDtos.cs

@@ -99,7 +99,10 @@ public sealed record TemplateScriptDto(
     string? ParameterDefinitions,
     string? ReturnDefinition,
     bool IsLocked,
-    TimeSpan? MinTimeBetweenRuns);
+    TimeSpan? MinTimeBetweenRuns,
+    // M2.5 (#9): per-script execution timeout (seconds). Additive trailing field;
+    // null on bundles written before this field existed.
+    int? ExecutionTimeoutSeconds = null);
 
 public sealed record TemplateCompositionDto(
     string InstanceName,