You don't swing the bat. You decide who does. Baseball GM puts you behind the desk of a big-league club and leaves you there. Ownership hands you a payroll and a goal — not a blank cheque. What happens next is entirely on your judgment: who you sign, who you draft, who you rush to the majors, and who you let walk in November. Every screen is a decision, not a menu. Spend $8M on a third baseman and you'll see exactly which rating it bought you. Promote a 22-year-old catcher a year early and…