Adds a full blackjack game with dealer AI, hit/stand/double-down actions,
and per-player payout multipliers (house-edge model). Extends the game
framework with manualStart support and a START_GAME WebSocket message so
hosts can begin when ready. Generalizes bet settlement transaction
descriptions from chess-specific to game-agnostic.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
