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/Settings/PaymentRuntime.php

@@ -341,7 +341,6 @@ class PaymentRuntime {
             'order_types_by_level' => $types_by_level,
             'disabled_code_stops_commission' => !empty($settings['affiliate_disabled_code_stops_commission']),
             'window_days' => (int) CreditsRuntime::get_referral_settings()['window_days'],
-            'settlement_days' => max(0, min(90, (int) ($settings['affiliate_settlement_days'] ?? 7))),
             'promotion_text' => sanitize_textarea_field((string) ($settings['pay_rebate_text_details'] ?? '')),
             'details_title' => sanitize_text_field((string) ($settings['pay_rebate_text_details_title'] ?? '返佣详解')),
             'poster' => [
@@ -375,10 +374,6 @@ class PaymentRuntime {
 		return (int) ($settings['ratios'][$key] ?? 0);
     }
     public static function get_affiliate_settings(): array { return self::get_payment_affiliate_settings(); }
-    public static function get_settlement_settings(): array {
-        $s = self::get_payment_affiliate_settings();
-        return ['observation_days' => (int) $s['settlement_days'], 'retry_limit' => 100];
-    }
 
     /**
      * Gateway channel selection. WeChat / Alipay each pick between the