1. create your app project in vs2012

2. add workflow to app project

3. make it a site workflow

those are the simple steps to add a workflow to a sharepoint 2013 app, it would be recommended to use vs2012 if your not! the workflow shouldnt be within the feature but within the app project!

full tut here:

http://blogs.msdn.com/b/officeapps/archive/2013/09/18/step-by-step-sending-email-messages-from-a-workflow-in-an-app-for-sharepoint-2013.aspx

1. create your app project in vs2012

2. add workflow to app project

3. make it a site workflow

those are the simple steps to add a workflow to a sharepoint 2013 app, it would be recommended to use vs2012 if your not! the workflow shouldnt be within the feature but within the app project!

full tut here:

http://blogs.msdn.com/b/officeapps/archive/2013/09/18/step-by-step-sending-email-messages-from-a-workflow-in-an-app-for-sharepoint-2013.aspx

EDIT

workflows are not added to the feature folder within vs2012!!!! they are added within the project like below:

its linked to the project that is linked to the feature, you can add a .cs class to the feature that overrieds the event items but that is it!

follow this link to make sure your correclty creating the app/workflow properly!

http://msdn.microsoft.com/en-us/library/office/dn456545.aspx