fix(revenue): drop 待偿欠款 from the commission card

The field rendered in two places on /user/revenue/: the 我的佣金 card's
meta line and the 累计佣金 row, both gated on a non-zero balance. Remove
both, along with the now-unused $debt_amount local and the dead
.uc-commission-card__debt rule.

Source trace, since the label is only the surface: CommissionLedger::
overview() reads debt_minor from aksrt_commission_debt and returns it as
'debt'; record_debt() books the shortfall when a refund cannot be clawed
back in full, and repay_debt_from_pool() later clears it out of the
commission pool. That mechanism is untouched — arrears still accrue and
still get repaid, the UI just no longer surfaces them. The reference
theme's rebate card has no equivalent concept, so this is not a parity
target either.

Keep 'debt' in the template's overview() fallback array: it mirrors the
real return shape and the repayment path still depends on the value.

Add a contract test asserting the label, its class and the local are gone
from the display layer while overview() keeps returning the key; verified
it fails if the label is reintroduced.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

assets/css/routes/user-center/revenue-earnings.css

@@ -110,13 +110,6 @@
   gap: 4px 16px;
 }
 
-/* 待偿欠款：退款收回不足挂账，副信息里以描边标签弱提示。 */
-.uc-content .uc-commission-card__debt {
-  padding: 0 8px;
-  border-radius: 999px;
-  background: rgba(255, 255, 255, .22);
-}
-
 /* 立即提现按钮：贴右居中，对齐参考主题 .abs-right。 */
 .uc-content .uc-commission-card__action {
   position: absolute;