Generate and store userId in client session

Of course, when userIds are generated before any voting occurs, everyone
will be given the same userId.  How can this be resolved?
Assign random userIds < 10000 when needed

Avoids having to keep track of users who have not voted
Vote posting implemented

Using post/redirect/get pattern, I think.  Messaging indicates
successful or failed submission.  Unfortunately, the user's bet value
selection does not persist.  This is a potential UX issue--options:
- store last bet in session
- lookup last bet on get and pass to form
Prevent access to nonexistent hands

In relevant handlers, return 404 if the indicated handId is not found in
the database.