fix: fix popup blocker and Select2 error when prefilling calendar

- Open window synchronously before await to avoid popup blocker,
  then navigate it to /Calendar/View after successful save; close
  it if the save fails
- Guard the #customer Select2 change handler so it bails early
  when #customer has not been initialized as Select2 yet

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

public/js/pages/Calendar/View.js

@@ -2378,6 +2378,8 @@ $(document).ready(function () {
 
     $('body').on('change', '#customer,#customer-info-type', function () {
 
+        if (!$('#customer').hasClass('select2-hidden-accessible')) return;
+
         if ($('#name').val() == "") {
             $('#name').val('IBN: ' + $("#customer").select2('data')[0].name);
         }