Manual retry option for failed subscription payments

Problem:
When a subscription payment fails, merchants currently have no way to manually trigger a retry — they're dependent on the automatic dunning/retry schedule. This delays recovery and gives merchants no control when a customer confirms they've fixed their payment method.

Proposed solution:
Add a "Retry now" action on failed subscription invoices/payments in the merchant dashboard, similar to Stripe's manual invoice retry. Merchant clicks retry → payment is attempted immediately against the customer's payment method on file → success/failure updates the invoice status and subscription state accordingly.