Add time forfeit adjudication in play mode

[Copilot]

When the user runs out of time during play mode, the game should be adjudicated as a loss, saved, and the engine quit — returning to neutral mode. This is configurable via Settings > Game.

Changes

• Time forfeit detection — In the human move loop, after each 100ms tick, checks human_timer.elapse >= human_timer.base. Shows a popup notifying the player, then breaks out of the game loop.
• Game result handling — Sets PGN Result to a loss for the forfeiting side and Termination to "{color} forfeits on time". Existing cleanup code handles engine quit and game save.
• Settings checkbox — Added "Adjudicate game on time forfeit" checkbox under Settings > Game, backed by self.is_time_forfeit_enabled (default: True).

# Core detection logic in the human move loop
if (self.is_time_forfeit_enabled and
        human_timer.elapse >= human_timer.base):
    sg.Popup('{} loses on time!'.format(color.capitalize()), ...)
    is_user_time_forfeit = True
    break