移除摸大红支付后建群逻辑，仅保留扫码与复制

支付成功只固化客服二维码与订单文案；同步清理迁移、配置与前后端相关字段。

frontend/src/features/mohong/views/MobileMohongOrderDetailView.vue

@@ -102,13 +102,6 @@ async function copyText() {
   }
 }
 
-function openChat() {
-  if (!order.value?.conversation_id) {
-    showToast({ message: '群聊尚未创建', icon: 'warning-o' })
-    return
-  }
-  router.push(`/chats/${order.value.conversation_id}`)
-}
 </script>
 
 <template>
@@ -177,16 +170,6 @@ function openChat() {
         >
           取消订单
         </van-button>
-        <van-button
-          v-if="order.conversation_id"
-          type="primary"
-          color="#ff6a00"
-          block
-          round
-          @click="openChat"
-        >
-          进入订单群
-        </van-button>
         <van-button v-if="order.copy_text" plain block round @click="copyText">
           复制订单信息
         </van-button>