anaagrams: Implement a game-ending modal

anaagrams: Implement a game-ending modal

Once the bag is empty and all players have gone idle, (nobody has even
attempted to claim a word in some time), the server will report that
the game is ready to end. The client then displays a modal with a
countdown giving the user the chance to say whether they are still
looking for words. If anyone is still looking, the server should start
its idle counter over. If not, then the server should declare the game
over.