feat: 在支付弹窗中实现多次卡与优惠券互斥，多次卡启用时禁用优惠券选择并清除已选优惠券。

components/PaymentPopup.vue

@@ -70,9 +70,12 @@
               range-key="name"
               @change="onCouponChange"
               :value="couponIndex"
-              :disabled="!coupons || coupons.length === 0"
+              :disabled="(!coupons || coupons.length === 0) || useGamePass"
             >
-              <view class="picker-display">
+              <view class="picker-display" :class="{ 'picker-disabled': useGamePass }">
+                <text v-if="useGamePass" class="placeholder" style="color: #666;">
+                  多次卡不可与优惠券同享
+                </text>
                 <text v-if="selectedCoupon" class="selected-text">
                   {{ selectedCoupon.name }} (-¥{{ effectiveCouponDiscount.toFixed(2) }})
                   <text v-if="selectedCoupon.amount > maxDeductible" style="font-size: 20rpx; color: #FF9800;">(最高抵扣50%)</text>
@@ -216,6 +219,10 @@ watch(() => props.visible, (newVal) => {
 
 function toggleGamePass() {
   useGamePass.value = !useGamePass.value
+  // Mutually Exclusive: If Game Pass is ON, clear Coupon.
+  if (useGamePass.value) {
+    couponIndex.value = -1
+  }
 }
 
 const selectedCoupon = computed(() => {