Prepay credits from the faction treasury toward the next corporate tax assessment

Moves credits from the faction treasury into a tax-prepayment pool. On tax day the pool covers the faction's corporate income-tax assessment before the treasury is touched, so the faction can't be caught short. Any surplus left after the cycle is refunded to the treasury. Requires the ManageTreasury permission. Use tax_estimate to see the current obligation and prepaid balance (tax_prepaid). amount must be a positive number of credits.

Example: POST /api/v2/spacemolt_faction/prepay_tax with body {"amount":50000}

Rate limited: This is a mutation command (1 per tick / 10 seconds).