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>

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

@@ -223,8 +223,8 @@ async function handleBuy() {
             <p>购买须知</p>
             <ul>
               <li>下单需登录并完成实名认证</li>
-              <li>支付成功后自动创建订单群，发送固定客服二维码</li>
-              <li>群内与订单详情可一键复制订单信息发给客服</li>
+              <li>支付成功后可在订单详情扫码联系客服</li>
+              <li>订单详情支持一键复制订单信息发给客服</li>
             </ul>
           </div>
         </div>

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

@@ -155,7 +155,7 @@ const activeCategoryName = () => {
       <div class="title-block">
         <h1>摸大红</h1>
         <span class="count">{{ total }} 件</span>
-        <span class="tip">{{ activeCategoryName() }} · 支付后自动进群</span>
+        <span class="tip">{{ activeCategoryName() }} · 支付后扫码联系客服</span>
       </div>
       <div class="actions">
         <div class="search-box">

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

@@ -123,13 +123,6 @@ async function copyText() {
   }
 }
 
-function openChat() {
-  if (!order.value?.conversation_id) {
-    ElMessage.warning('群聊尚未创建')
-    return
-  }
-  router.push(`/messages/${order.value.conversation_id}`)
-}
 </script>
 
 <template>
@@ -197,14 +190,6 @@ function openChat() {
           >
             取消订单
           </button>
-          <button
-            v-if="order.conversation_id"
-            type="button"
-            class="btn outline"
-            @click="openChat"
-          >
-            进入订单群
-          </button>
           <button v-if="order.copy_text" type="button" class="btn outline" @click="copyText">
             复制订单信息
           </button>