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.Commons/Types/Flattening/FlattenedConfiguration.cs

@@ -174,6 +174,14 @@ public sealed record ResolvedScript
 
     /// <summary>Gets the minimum time between script executions.</summary>
     public TimeSpan? MinTimeBetweenRuns { get; init; }
+
+    /// <summary>
+    /// Per-script execution timeout in seconds, or null to use the site's global
+    /// default. A non-positive value is treated as null (use global) by the Site
+    /// Runtime. Seconds (not TimeSpan) to match the global option it overrides.
+    /// </summary>
+    public int? ExecutionTimeoutSeconds { get; init; }
+
     /// <summary>Gets the source of this script.</summary>
     public string Source { get; init; } = "Template";