...The row of cards can be deleted as sum (add/subtract) of cards is 0. (J is 11,Q is 12, K is 13)
If the number of cards is 12, but can't be deleted now.
The game is over. By the way, if cards library is empty and user can't win,
the game is over.
v0.1.1 Update:
You can move an entire pile to another pile (except the first card).
If the front half of a pile becomes 0 after applying + / −, you must click the next card pile (the card immediately after that 0) to auto-remove