feat: Add ActiveAdmin 4 and Propshaft support

- Switch to ActiveAdmin 4 beta with Tailwind CSS
- Replace Sprockets with Propshaft for Rails 8
- Migrate from jQuery to vanilla JavaScript
- Implement proper module initialization without setTimeout hacks
- Add esbuild for JavaScript bundling with clean import aliases
- Configure Tailwind CSS build process with ActiveAdmin plugin
- Update engine configuration for both Propshaft and Sprockets
- Add comprehensive documentation for AA4 gem updates
- Maintain backward compatibility with legacy AA versions

🤖 Generated with Claude Code

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

spec/support/javascript_helper.rb

@@ -0,0 +1,118 @@
+# frozen_string_literal: true
+
+module JavaScriptHelper
+  def ensure_quill_loaded
+    # Wait for Quill to be available
+    Timeout.timeout(10) do
+      loop do
+        quill_loaded = page.evaluate_script('typeof Quill !== "undefined"')
+        break if quill_loaded
+        sleep 0.1
+      end
+    end
+
+    # Wait for initialization script to be loaded
+    Timeout.timeout(10) do
+      loop do
+        init_loaded = page.evaluate_script(<<~JS)
+          typeof getQuillEditors === 'function' &&
+          typeof getQuillEditorByIndex === 'function' &&
+          typeof getQuillEditorByElementId === 'function'
+        JS
+        break if init_loaded
+        sleep 0.1
+      end
+    end
+  rescue Timeout::Error
+    raise 'Quill editor failed to load within timeout'
+  end
+
+  def wait_for_quill_editor(selector = '[data-aa-quill-editor]')
+    expect(page).to have_css(selector, wait: 5)
+    ensure_quill_loaded
+
+    # Wait for the editor to be initialized
+    page.evaluate_script(<<~JS)
+      (function() {
+        const editor = document.querySelector('#{selector}');
+        if (!editor || !editor._quillEditor) return false;
+        return true;
+      })()
+    JS
+  end
+
+  def get_quill_content(index = 0)
+    page.evaluate_script("getQuillEditorByIndex(#{index})?.root.innerHTML")
+  end
+
+  def set_quill_content(content, index = 0)
+    page.evaluate_script(<<~JS)
+      (function() {
+        const editor = getQuillEditorByIndex(#{index});
+        if (editor) {
+          editor.root.innerHTML = '#{content.gsub("'", "\\\\'")}';
+          return true;
+        }
+        return false;
+      })()
+    JS
+  end
+
+  def format_quill_text(format, index = 0)
+    page.evaluate_script(<<~JS)
+      (function() {
+        const editor = getQuillEditorByIndex(#{index});
+        if (editor) {
+          editor.selectAll();
+          editor.format('#{format}', true);
+          return true;
+        }
+        return false;
+      })()
+    JS
+  end
+
+  def insert_quill_text(text, index = 0)
+    page.evaluate_script(<<~JS)
+      (function() {
+        const editor = getQuillEditorByIndex(#{index});
+        if (editor) {
+          const length = editor.getLength();
+          editor.insertText(length - 1, '#{text.gsub("'", "\\\\'")}');
+          return true;
+        }
+        return false;
+      })()
+    JS
+  end
+
+  def quill_editor_count
+    page.evaluate_script('getQuillEditors().length')
+  end
+
+  def quill_has_content?(text, index = 0)
+    content = get_quill_content(index)
+    return false unless content
+    content.include?(text)
+  end
+
+  def click_quill_toolbar_button(button_class, index = 0)
+    page.evaluate_script(<<~JS)
+      (function() {
+        const editors = document.querySelectorAll('[data-aa-quill-editor]');
+        if (editors[#{index}]) {
+          const button = editors[#{index}].querySelector('.ql-toolbar .#{button_class}');
+          if (button) {
+            button.click();
+            return true;
+          }
+        }
+        return false;
+      })()
+    JS
+  end
+end
+
+RSpec.configure do |config|
+  config.include JavaScriptHelper, type: :system
+end