WebSocket Game Controller

[Pranux]

• Create GameWebSocketController with @MessageMapping
• Handle /app/game/{roomId}/start - Start game
• Handle /app/game/{roomId}/clue - Submit clue
• Handle /app/game/{roomId}/guess - Submit guess
• Handle /app/game/{roomId}/next - Next round
• Implement @sendto("/topic/game/{roomId}") for broadcasting state