RHOAIENG-58422: Replace magic number check with semantic user-message check

Address review feedback by replacing `messages.length <= 1` with an
explicit check for user messages (`!messages.some(m => m.role === 'user')`).
This eliminates the magic number that depended on knowing the initial bot
message always occupies index 0, making the intent clear: the welcome
prompt hides only when a user has actually sent a message. Added a test
for the empty-messages edge case.

The CI failures (Contract-Tests, test-and-build) were caused by a
transient npm ETIMEDOUT in model-registry install and a pre-existing
flaky mcpTab Cypress test — neither is related to this change.

Closes RHOAIENG-58422

Co-Authored-By: Claude <noreply@anthropic.com>
Signed-off-by: Nick Gagan <ngagan@redhat.com>

Author: jira-autofix-bot

packages/gen-ai/frontend/src/app/Chatbot/ChatbotConfigInstance.tsx

@@ -136,7 +136,7 @@ export const ChatbotConfigInstance: React.FC<ChatbotConfigInstanceProps> = ({
 
   return (
     <MessageBox position="top">
-      {showWelcomePrompt && messagesHook.messages.length <= 1 && (
+      {showWelcomePrompt && !messagesHook.messages.some((m) => m.role === 'user') && (
         <ChatbotWelcomePrompt
           title={username ? `Hello, ${username}` : 'Hello'}
           description={welcomeDescription}

packages/gen-ai/frontend/src/app/Chatbot/__tests__/ChatbotConfigInstance.spec.tsx

@@ -129,13 +129,19 @@ describe('ChatbotConfigInstance', () => {
       mockMessages = [];
     });
 
-    it('should show welcome prompt when showWelcomePrompt is true and no real messages exist', () => {
+    it('should show welcome prompt when showWelcomePrompt is true and no user messages exist', () => {
       mockMessages = [{ id: '1', role: 'bot', content: 'placeholder' }];
       render(<ChatbotConfigInstance {...defaultProps} showWelcomePrompt />);
       expect(screen.getByTestId('chatbot-welcome-prompt')).toBeInTheDocument();
     });
 
-    it('should hide welcome prompt when real messages exist', () => {
+    it('should show welcome prompt when messages array is empty', () => {
+      mockMessages = [];
+      render(<ChatbotConfigInstance {...defaultProps} showWelcomePrompt />);
+      expect(screen.getByTestId('chatbot-welcome-prompt')).toBeInTheDocument();
+    });
+
+    it('should hide welcome prompt when a user message exists', () => {
       mockMessages = [
         { id: '1', role: 'bot', content: 'placeholder' },
         { id: '2', role: 'user', content: 'Hello' },