feat(revenue): immediate commission credit with independent withdrawable pool

Aligns affiliate commission with the reference theme: commission is credited
to a dedicated COMMISSION asset pool the moment an order is paid, removing the
7-day settlement freeze, the settlement cron, and the settlement_days setting.

- Ledger: add AssetType::COMMISSION (isolated from the recharge balance wallet)
- CommissionLedger: credit-on-record + opportunistic debt repayment; refunds
  claw back the full commission from the pool, carrying any shortfall as debt
  (aksrt_commission_debt) that future commission pays down first
- Withdrawal: make asset-aware via a source discriminator (commission vs
  balance); each pool keeps independent daily limits, pending gate, and
  reject-refund. Balance withdrawal (recharge + creator income) is unchanged
- Fix pay_rebate_self_s: honor self-commission at purchase time
- Revenue card: show pool balance + 累计/已提现 (drop 待结算), debt when present
- Schema 2.0.0 -> 2.1.0: add commission_debt, drop freeze columns

src/Core/DBMigratorPart3.php

@@ -37,6 +37,7 @@ trait DBMigratorPart3 {
             'affiliate_relation' => 'aksrt_affiliate_relation',
             'commission_ledger' => 'aksrt_commission_ledger',
             'commission_adjustment' => 'aksrt_commission_adjustment',
+            'commission_debt' => 'aksrt_commission_debt',
             'payout_account' => 'aksrt_payout_account',
             'coupon_usage'         => 'aksrt_coupon_usage',
             'user_restriction'     => 'aksrt_user_restriction',