fix: 修复BepUsdt签名错误和待支付订单付款入口

- payment.go: 添加timestamp字段到签名和请求体(参照官方epusdt实现)
- payment.go: 修复amount格式化,使用strconv.FormatFloat替代Sprintf
- payment.go: 修复expiration_time处理(毫秒转秒,计算剩余秒数)
- payment.go: 修复apiURL尾部斜杠处理
- OrderDetail.vue: 添加去支付按钮(pending_payment状态)
- Orders.vue: 添加去支付按钮(bepusdt跳转收银台)

frontend/src/views/user/OrderDetail.vue

@@ -6,6 +6,7 @@
       <div class="status-section">
         <el-tag :type="statusType(order.status)" size="large">{{ statusText(order.status) }}</el-tag>
         <span v-if="order.payment_method" class="payment-method">支付方式: {{ paymentMethodText(order.payment_method) }}</span>
+        <el-button v-if="order.status === 'pending_payment'" type="primary" @click="goPay">去支付</el-button>
       </div>
       
       <div class="section-title">订单信息</div>
@@ -57,12 +58,13 @@
 
 <script setup lang="ts">
 import { ref, computed, onMounted } from 'vue'
-import { useRoute } from 'vue-router'
+import { useRoute, useRouter } from 'vue-router'
 import { ElMessage } from 'element-plus'
 import { orderApi } from '../../api'
 import BackNav from '../../components/BackNav.vue'
 
 const route = useRoute()
+const router = useRouter()
 const order = ref<any>(null)
 const showRefund = ref(false)
 const refundReason = ref('')
@@ -108,6 +110,14 @@ onMounted(async () => {
   order.value = res.data
 })
 
+function goPay() {
+  if (order.value?.payment_method === 'bepusdt') {
+    router.push(`/checkout/${order.value.id}`)
+  } else {
+    ElMessage.info('请联系客服完成支付')
+  }
+}
+
 async function applyRefund() {
   if (!refundReason.value.trim()) {
     ElMessage.warning('请填写退款原因')

frontend/src/views/user/Orders.vue

@@ -18,6 +18,7 @@
         <el-table-column label="操作" width="200">
           <template #default="{ row }">
             <el-button link type="primary" size="small" @click="$router.push(`/orders/${row.id}`)">查看</el-button>
+            <el-button v-if="row.status === 'pending_payment'" link type="success" size="small" @click="goPay(row)">去支付</el-button>
             <el-button v-if="row.status === 'pending_payment' || row.status === 'pending_confirm'" link type="warning" size="small" @click="cancelOrder(row.id)">取消</el-button>
             <el-button v-if="row.status === 'shipped'" link type="success" size="small" @click="confirmReceipt(row.id)">确认收货</el-button>
           </template>
@@ -29,10 +30,12 @@
 
 <script setup lang="ts">
 import { ref, onMounted } from 'vue'
+import { useRouter } from 'vue-router'
 import { ElMessage, ElMessageBox } from 'element-plus'
 import { orderApi } from '../../api'
 import BackNav from '../../components/BackNav.vue'
 
+const router = useRouter()
 const orders = ref<any[]>([])
 
 const statusMap: Record<string, string> = {
@@ -66,6 +69,14 @@ async function fetchOrders() {
   }
 }
 
+function goPay(row: any) {
+  if (row.payment_method === 'bepusdt') {
+    router.push(`/checkout/${row.id}`)
+  } else {
+    ElMessage.info('请联系客服完成支付')
+  }
+}
+
 async function cancelOrder(id: number) {
   try {
     await ElMessageBox.confirm('确定要取消该订单吗？', '提示', { type: 'warning' })