fix: Update tests and CI for ActiveAdmin 4 compatibility

- Fix active_admin_comments to use active_admin_comments_for in AA4
- Add author to CSS test to fix validation error
- Update has_many support for AA4 using .has-many-add button click
- Simplify GitHub Actions workflow for AA4 testing
- All tests now passing with ActiveAdmin 4.0.0.beta16

🤖 Generated with Claude Code

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

vendor/assets/javascripts/activeadmin_quill_editor.js

@@ -190,10 +190,16 @@
     document.addEventListener('turbolinks:load', initQuillEditors);
 
     // Support for ActiveAdmin has_many fields
-    document.addEventListener('has_many_add:after', function(event) {
-      const newFields = event.target.querySelectorAll('[data-aa-quill-editor]');
-      newFields.forEach(initQuillEditor);
-      setupFormSubmission();
+    // ActiveAdmin 4 uses .has-many-add button click
+    document.addEventListener('click', function(event) {
+      if (event.target.closest('.has-many-add')) {
+        // Wait for DOM to be updated with new fields
+        setTimeout(function() {
+          const newEditors = document.querySelectorAll('[data-aa-quill-editor]:not(.quill-editor--active)');
+          newEditors.forEach(initQuillEditor);
+          setupFormSubmission();
+        }, 10);
+      }
     });
   }