fix(im): 修复历史退群群未读和成员加载问题

- 已读上报使用会话末条消息编号兜底
- 历史退群群不再请求群成员列表
- 群聊 read 放开当前成员校验，保留可见性校验
- Vben 群详情补齐 joinStatus
- 补充退群群已读边界测试

src/views/im/home/pages/conversation/components/message/MessagePanel.vue

@@ -437,12 +437,15 @@ const groupMembers = computed<GroupMemberLite[]>(() => {
   })
 })
 
-/** 切换到群会话时同步群信息 + 成员；各自 fire-and-forget + catch，任何一项失败不牵连其它 */
+/** 切换到群会话时同步群信息 + 成员 */
 async function ensureGroupData(groupId: number) {
-  // 远程异步拉群信息（群名 / 公告 / 群主等元数据）
-  groupStore.fetchGroupInfo(groupId).catch((error) => {
+  // 远程拉群信息（群名 / 公告 / 群主等元数据）
+  await groupStore.fetchGroupInfo(groupId).catch((error) => {
     console.warn('[IM MessagePanel] fetchGroupInfo 失败', { groupId }, error)
   })
+  if (isGroupQuit(groupStore.getGroup(groupId))) {
+    return
+  }
 
   // 先从 IDB 同步加载群成员，让首帧立即出成员名 / 头像
   await groupStore.loadGroupMemberList(groupId).catch((error) => {

src/views/im/home/store/messageStore.ts

@@ -27,7 +27,7 @@ import {
 } from '../../utils/message'
 import { resolveConversationLastContent } from '../../utils/conversation'
 import { getCurrentUserId } from '@/utils/auth'
-import { tryGetSenderDisplayName } from '../../utils/user'
+import { isGroupQuit, tryGetSenderDisplayName } from '../../utils/user'
 import { useGroupStore } from './groupStore'
 import { useConversationStore } from './conversationStore'
 import type { ImConversationReadRespVO } from '@/api/im/conversation/read'
@@ -137,6 +137,9 @@ function deriveLastSenderDisplayName(
   if (conversation.type === ImConversationType.GROUP) {
     const groupStore = useGroupStore()
     const group = groupStore.getGroup(conversation.targetId)
+    if (isGroupQuit(group)) {
+      return conversation.lastSenderId === senderId ? conversation.lastSenderDisplayName : undefined
+    }
     const fetchPromise =
       group?.membersLoaded && !group.membersExpired
         ? groupStore.fetchGroupMember(conversation.targetId, senderId)