chore: Add a condition to handle bounced email (#11873)

Add bounced emails to the conversation thread.
Fix Gmail bounce detection by checking the X-Failed-Recipients header.

Currently, bounced emails are rejected as auto-replies, which causes
support agents to miss important delivery failure context. This PR
ensures bounced messages are correctly added to the thread, preserving
visibility for the support team.

app/presenters/mail_presenter.rb

@@ -157,6 +157,10 @@ class MailPresenter < SimpleDelegator
     auto_submitted? || x_auto_reply?
   end
 
+  def bounced?
+    @mail.bounced? || @mail['X-Failed-Recipients'].try(:value).present?
+  end
+
   def notification_email_from_chatwoot?
     # notification emails are send via mailer sender email address. so it should match
     original_sender == Mail::Address.new(ENV.fetch('MAILER_SENDER_EMAIL', 'Chatwoot <accounts@chatwoot.com>')).address