修改名称，优化

cloudfunctions/joinRoom/index.js

@@ -27,9 +27,17 @@ exports.main = async (event, context) => {
         const members = room.data.members || []
         const isMember = members.some(m => m.openid === openid)
 
-        if (!isMember) {
-            // 加入房间
-            const newMember = {
+        if (isMember) {
+            return { success: true, msg: '已在房间内' }
+        }
+
+        // 检查人数限制（最多8人）
+        if (members.length >= 8) {
+            return { success: false, msg: '房间人数已满（最多8人）' }
+        }
+
+        // 加入房间
+        const newMember = {
                 openid: openid,
                 avatarUrl: userInfo?.avatarUrl || 'https://mmbiz.qpic.cn/mmbiz/icTdbqWNOwNRna42FI242Lcia07jQodd2FJGIYQfG0LAJGFxM4FbnQP6yfMxBgJ0F3YRqJCJ1aPAK2dQagdusBZg/0',
                 nickName: userInfo?.nickName || '微信用户',