fix: 群聊@人员改用markdown消息，解决他人看到原始userid问题

appchat text消息的<@userid>语法对非本人显示为原始文本，
改用markdown消息类型发送@提醒

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

app/services/wechat_service.py

@@ -357,7 +357,7 @@ class WeChatService:
             return None
 
     async def send_group_text(self, chat_id: str, content: str) -> bool:
-        """发送文本消息到群聊（支持 <@userid> 语法 @人员）"""
+        """发送文本消息到群聊"""
         if not self._enabled:
             return False
         try:
@@ -380,6 +380,30 @@ class WeChatService:
             logger.error(f"发送群聊文本异常: {e}")
             return False
 
+    async def send_group_markdown(self, chat_id: str, content: str) -> bool:
+        """发送 markdown 消息到群聊（@人员使用此方式）"""
+        if not self._enabled:
+            return False
+        try:
+            access_token = await self._get_access_token()
+            msg = {
+                "chatid": chat_id,
+                "msgtype": "markdown",
+                "markdown": {"content": content},
+            }
+            url = f"https://qyapi.weixin.qq.com/cgi-bin/appchat/send?access_token={access_token}"
+            async with httpx.AsyncClient(timeout=10) as client:
+                resp = await client.post(url, json=msg)
+                data = resp.json()
+            if data.get("errcode") != 0:
+                logger.error(f"群聊markdown发送失败: {data}")
+                return False
+            logger.info(f"群聊markdown已发送: chatid={chat_id}")
+            return True
+        except Exception as e:
+            logger.error(f"发送群聊markdown异常: {e}")
+            return False
+
     async def send_group_image(self, chat_id: str, media_id: str) -> bool:
         """发送图片消息到群聊"""
         if not self._enabled:
@@ -500,11 +524,11 @@ class WeChatService:
         if not sent:
             success = False
 
-        # ---- 3. @相关人员（text 消息） ----
+        # ---- 3. @相关人员（markdown 消息，@渲染更可靠） ----
         if mention_user_ids:
             mentions = " ".join(f"<@{uid}>" for uid in mention_user_ids)
-            text_content = f"{mentions} 请及时处理以上{type_name}告警"
+            md_content = f"{mentions} 请及时处理以上**{type_name}告警**"
-            sent = await self.send_group_text(chat_id, text_content)
+            sent = await self.send_group_markdown(chat_id, md_content)
             if not sent:
                 success = False