✨ feat: implement backend channel duplication & streamline frontend copy flow

Add a dedicated backend endpoint to clone an existing channel (including its key) and
replace all previous front-end cloning logic with a single API call.

Backend
• controller/channel.go
  – add CopyChannel: safely clone a channel, reset balance/usage, append name suffix,
    preserve key, create abilities, return new ID.
  – supports optional query params: `suffix`, `reset_balance`.
• router/api-router.go
  – register POST /api/channel/copy/:id (secured by AdminAuth).
• model interaction uses BatchInsertChannels to ensure transactional integrity.

Frontend
• ChannelsTable.js
  – simplify copySelectedChannel: call /api/channel/copy/{id} and refresh list.
  – remove complex field-manipulation & key-fetching logic.
  – improved error handling.

Security & stability
• All cloning done server-side; sensitive key never exposed to client.
• Route inherits existing admin middleware.
• Graceful JSON responses with detailed error messages.

web/src/components/table/ChannelsTable.js

@@ -964,28 +964,16 @@ const ChannelsTable = () => {
   };
 
   const copySelectedChannel = async (record) => {
-    const channelToCopy = { ...record };
-    channelToCopy.name += t('_复制');
-    channelToCopy.created_time = null;
-    channelToCopy.balance = 0;
-    channelToCopy.used_quota = 0;
-    delete channelToCopy.test_time;
-    delete channelToCopy.response_time;
-    if (!channelToCopy) {
-      showError(t('渠道未找到，请刷新页面后重试。'));
-      return;
-    }
     try {
-      const newChannel = { ...channelToCopy, id: undefined };
-      const response = await API.post('/api/channel/', newChannel);
-      if (response.data.success) {
+      const res = await API.post(`/api/channel/copy/${record.id}`);
+      if (res?.data?.success) {
         showSuccess(t('渠道复制成功'));
         await refresh();
       } else {
-        showError(response.data.message);
+        showError(res?.data?.message || t('渠道复制失败'));
       }
     } catch (error) {
-      showError(t('渠道复制失败: ') + error.message);
+      showError(t('渠道复制失败: ') + (error?.response?.data?.message || error?.message || error));
     }
   };