When planning multi-year budgets, teams need to create payment methods in advance, one per year. Without a start date, there is no way to prevent a payment method from being used before its designated period begins, making it impossible to enforce correct budget allocation across time.

Add an optional active start date to payment methods. A payment method with a future start date cannot be assigned to or used by any project until that date is reached. This allows operators and workspace owners to pre-create a full set of time-bounded payment methods and rely on meshStack to enforce the correct one for each period.