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/admin/views/AdminMohongConfigView.vue

@@ -14,7 +14,6 @@ const loading = ref(false)
 const saving = ref(false)
 const form = reactive<MohongConfig>({
   default_qrcode_url: '',
-  group_welcome_text: '',
   order_copy_template: '',
 })
 
@@ -37,7 +36,6 @@ async function handleSave() {
   try {
     const config = await updateAdminMohongConfig({
       default_qrcode_url: form.default_qrcode_url,
-      group_welcome_text: form.group_welcome_text,
       order_copy_template: form.order_copy_template,
     })
     Object.assign(form, config)
@@ -66,7 +64,7 @@ async function uploadQrcode(file: File) {
     <div class="page-head">
       <div>
         <h2>摸大红配置</h2>
-        <p>全局默认固定二维码、群欢迎语、订单复制模板。商品可覆盖默认二维码。</p>
+        <p>全局默认固定二维码与订单复制模板。商品可覆盖默认二维码；支付后用户在订单详情扫码并复制信息联系客服。</p>
       </div>
       <el-button type="primary" :loading="saving" @click="handleSave">保存配置</el-button>
     </div>
@@ -88,9 +86,6 @@ async function uploadQrcode(file: File) {
           </div>
         </div>
       </el-form-item>
-      <el-form-item label="群欢迎语">
-        <el-input v-model="form.group_welcome_text" type="textarea" :rows="3" />
-      </el-form-item>
       <el-form-item label="复制文案模板">
         <el-input v-model="form.order_copy_template" type="textarea" :rows="8" />
         <div class="hint">

frontend/src/features/admin/views/AdminMohongOrdersView.vue

@@ -174,9 +174,6 @@ async function copyText(text: string) {
           <el-descriptions-item label="买家">
             {{ detail.buyer_nickname }} {{ detail.buyer_phone }}
           </el-descriptions-item>
-          <el-descriptions-item label="会话ID">
-            {{ detail.conversation_id || '-' }}
-          </el-descriptions-item>
         </el-descriptions>
         <div v-if="detail.copy_text" class="copy-box">
           <div class="copy-head">