chore: improve workflow names and fix CSS indentation consistency (#18)

* fix: resolve plugin class loading reliability issues

* fix: address CodeRabbit XSS and accessibility findings from PR #18

- admin/js/admin-scripts.js: replace HTML string interpolation in showNotice
  with DOM API construction and .text() to prevent XSS; whitelist type values
- admin/js/update-source-selector.js: replace .html(message) with .text(message)
  in showMessage to prevent XSS from AJAX response content
- admin/templates/modal.php: add role=dialog, aria-modal=true, aria-labelledby
  for screen reader semantics; replace <span> close control with <button> for
  keyboard operability and proper ARIA role

admin/js/update-source-selector.js

@@ -153,8 +153,8 @@
     showMessage: function (type, message) {
       const $message = this.$modal.find( '.wpst-modal-message' );
 
-      // Set message content and type.
-      $message.html( message ).removeClass( 'success error' ).addClass( type ).show();
+      // Set message as plain text to prevent XSS, then apply type class.
+      $message.text( message ).removeClass( 'success error' ).addClass( type ).show();
 
       // Hide message after a delay for success messages.
       if (type === 'success') {