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

tests/widget-system/asset-ledger-contract.test.cjs

@@ -135,7 +135,7 @@ test('core asset paths never use floating-point money helpers', () => {
 test('points orders bypass cash commissions and purchase dead paths stay removed', () => {
   const commission = fs.readFileSync(path.join(root, 'src', 'Payment', 'CommissionLedger.php'), 'utf8')
   const paidStart = commission.indexOf('public function record_paid_order')
-  const paidEnd = commission.indexOf('public function settle_due', paidStart)
+  const paidEnd = commission.indexOf('private function credit_commission', paidStart)
   const paidMethod = commission.slice(paidStart, paidEnd)
   const pointsGuard = paidMethod.indexOf('AssetType::POINTS->value')
   const affiliateGuard = paidMethod.indexOf('Settings::affiliate_enabled()')