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.ConfigurationDatabase/Configurations/TemplateConfiguration.cs

@@ -178,6 +178,11 @@ public class TemplateScriptConfiguration : IEntityTypeConfiguration<TemplateScri
         builder.Property(s => s.ReturnDefinition)
             .HasMaxLength(4000);
 
+        // M2.5 (#9): nullable per-script execution timeout (seconds). Null = use
+        // the site's global ScriptExecutionTimeoutSeconds default.
+        builder.Property(s => s.ExecutionTimeoutSeconds)
+            .IsRequired(false);
+
         builder.HasIndex(s => new { s.TemplateId, s.Name }).IsUnique();
     }
 }