You are very correct. Old habits die hard.
Semantic UI - http://semantic-ui.com/
Foundation -http://foundation.zurb.com/
Here are the two main alternatives that I would consider.
However, if you have a good designer on your team, you may want to consider a more lightweight responsive framework instead of these kitchen-sink-included.
Great topic, will be added to my list of upcoming episodes!
My apologies. I haven't found any solid ones yet. However, you can use ink for emails without interfering with the bootstrap web app. It could be something as simple as creating a bootstrap CSS file in place of the foundation one.
It's a strange situation where you have two acting parts. The initial form when creating a new contact would trigger the date picker from turbolinks:load. However, when you go to edit the contact, the turbolinks:load would not trigger since it is a server generated javascript being sent back. In hindsight, the document.ready should be removed from the date_picker_init.js file and placed under the edit.js.erb since it is more applicable there.