修复群聊解散通知覆盖不全：主动退出/解散群聊会误报"该群聊已解散"且留下幽灵会话

前情：上一版修复只覆盖了"被动看着群被别人解散"这一种场景（后端走自定义
{info what:"group" event:"group.dissolved"}事件而非原生{pres what:"gone"}，
需要单独识别）。这次用户实测发现同一个"话题彻底消失后清理不干净"的问题在另外
两条路径上都复现了：自己点"退出群聊"、自己（群主）点"解散群聊"。

根因：这两个操作各自的mutation.onSuccess只是navigate('/messages')，没有做任何
本地缓存清理；而服务端在REST调用成功后，通常还会异步地给这条已经不再属于你的
订阅补发一个原生/自定义的"gone"信号——这个信号触发的是topics.ts里那条本该只用
于"被动围观"场景的goneListeners通知链，于是ConversationView的通用"该群聊已
解散"提示被复用到了并不贴切的"我自己退出/解散"场景上，且同一个SDK缓存stub没
被清理的老毛病（getTopic()被再次调用就会重建一个空壳）也照样在这两条路径上
重演，表现为消息列表里多出一个显示原始群ID、"1970/1/1"的幽灵会话。

修复：
- topics.ts的markTopicGoneAndNotify新增goneTopicNames去重判断——只要
  forgetTopic已经先标记过这个话题，稍后到达的原生/自定义gone信号就直接跳过
  （包括不再触发goneListeners），避免重复通知。
- GroupDetailColumn.tsx的leaveMutation/disbandMutation改成onSuccess里先调用
  forgetTopic(topicId)（清缓存+加入排除名单+让上面的守卫生效）再navigate，
  不再空等异步信号来做清理。

实机验证：systest04建群拉systest02入群 -> systest02主动退出，返回消息列表后
侧栏不再残留幽灵会话；systest04（群主）解散同一个群，同样返回消息列表且侧栏
干净。顺带在GroupDetailColumn.tsx里把群头像/成员格子头像接上了真实上传头像
（见下一条commit的头像修复，这个文件因为改动集中放在了一起）。

web/src/features/groups/GroupDetailColumn.tsx

@@ -3,6 +3,7 @@ import { useLayoutEffect, useState } from 'react';
 import { useMutation, useQuery, useQueryClient } from '@tanstack/react-query';
 import { useNavigate } from 'react-router-dom';
 
+import { Avatar } from '@/app/Avatar';
 import { Icon } from '@/app/Icon';
 import { Toast } from '@/app/Toast';
 import { QRCodeModal } from '@/features/contacts/QRCodeModal';
@@ -24,8 +25,8 @@ import {
   type GroupSettings,
 } from '@/lib/api/groups';
 import type { MediaType } from '@/lib/api/messages';
-import { avatarBgClass, avatarLetter } from '@/lib/avatar';
 import { useTinode } from '@/lib/tinode/hooks';
+import { forgetTopic } from '@/lib/tinode/topics';
 import { requestConfirm } from '@/stores/confirmDialog';
 import { notify } from '@/stores/globalToast';
 import { requestActionToken } from '@/stores/securityChallenge';
@@ -151,15 +152,30 @@ export function GroupDetailColumn({ topicId, peerName, onClose, onOpenHistory }:
     onError: (err) => showError(err, '昵称保存失败'),
   });
 
+  // Both mutations call forgetTopic() the instant their own REST call succeeds, rather than waiting
+  // on the async native/`group.dissolved` gone-signal that normally follows a group actually going
+  // away -- real, user-reported bugs fixed by this: (1) the chat list kept showing a broken stale
+  // stub for this group after leaving/disbanding it (same lingering-stub symptom `forgetTopic` was
+  // originally built to fix for the refresh/404 case, just reached via a third path); (2) that same
+  // late signal, left unguarded, used to re-fire ConversationView's generic "该群聊已解散" toast on
+  // top of this action's own navigate -- wrong wording specifically for 退出群聊 (leaving yourself
+  // isn't the group being dissolved). `markTopicGoneAndNotify`'s own guard (topics.ts) now skips that
+  // late signal entirely once `forgetTopic` has already marked this name gone here.
   const leaveMutation = useMutation({
     mutationFn: () => leaveGroup(topicId),
-    onSuccess: () => navigate('/messages'),
+    onSuccess: () => {
+      forgetTopic(topicId);
+      navigate('/messages');
+    },
     onError: (err) => showError(err, '退出群聊失败'),
   });
 
   const disbandMutation = useMutation({
     mutationFn: (actionToken: string) => disbandGroup(topicId, actionToken),
-    onSuccess: () => navigate('/messages'),
+    onSuccess: () => {
+      forgetTopic(topicId);
+      navigate('/messages');
+    },
     onError: (err) => showError(err, '解散群聊失败'),
   });
 
@@ -237,9 +253,12 @@ export function GroupDetailColumn({ topicId, peerName, onClose, onOpenHistory }:
         <div className="bg-white md:contents">
           <div className="flex flex-col gap-2 px-4 py-4 md:border-b md:border-border-list-item md:px-5">
             <div className="flex items-center gap-3">
-              <span className={`grid h-13 w-13 flex-none place-items-center rounded-xl text-xl font-medium text-white ${avatarBgClass(topicId)}`}>
-                {avatarLetter(groupQuery.data?.name || peerName)}
-              </span>
+              <Avatar
+                id={topicId}
+                name={groupQuery.data?.name || peerName}
+                avatarFileId={groupQuery.data?.avatar_file_id}
+                className="h-13 w-13 flex-none rounded-xl text-xl"
+              />
               <div className="flex min-w-0 flex-col">
                 <strong className="truncate text-base font-semibold text-text-heading">{groupQuery.data?.name || peerName}</strong>
                 <span className="text-xs text-text-tertiary-2">
@@ -274,11 +293,12 @@ export function GroupDetailColumn({ topicId, peerName, onClose, onOpenHistory }:
                 <div key={m.user_id} className="relative flex flex-col items-center gap-1">
                   {/* README §4.10/#1e: mobile member-grid avatars are 44px, one size up from
                       desktop's 40px (unconditional here before this fix). */}
-                  <span
-                    className={`grid h-11 w-11 place-items-center rounded-lg text-sm font-medium text-white md:h-10 md:w-10 ${avatarBgClass(m.user_id)}`}
-                  >
-                    {avatarLetter(m.display_name)}
-                  </span>
+                  <Avatar
+                    id={m.user_id}
+                    name={m.display_name}
+                    avatarFileId={m.avatar_file_id}
+                    className="h-11 w-11 rounded-lg text-sm md:h-10 md:w-10"
+                  />
                   <RoleCorner role={m.role} />
                   <span className="w-full truncate text-center text-[11px] text-text-secondary">{m.display_name || m.user_id}</span>
                 </div>