fix(web): 第9轮审查批次2——群聊域一批问题

- 建群留空群名字直接被后端拒绝：placeholder写的"未填写时默认为成员
  昵称组合"从未真正实现，现在留空时用已选成员昵称拼接生成默认名，
  按MAX_TITLE_LENGTH截断
- 群文件上传按钮不受"群文件上传权限"治理开关约束：新增canUpload
  （和canInvite同一个算法），仅管理员时非管理员看不到上传入口
- 群管理弹层5个治理开关（进群验证/全员禁言/文件上传/私聊权限/邀请
  权限）都没有读取后端返回的对应_editable字段，现在全部接上
- 禁言成员列表只拉第一页：新增getAllGroupMutes复用fetchAllPages，
  和getAllGroupMembers同一个模式，人数多的群不会再静默截断
- 添加管理员没有前端数量上限校验：达到上限时按钮禁用并提示"已达
  管理员人数上限"，不再让用户选完人才被后端拒绝
- 清空聊天记录没有错误处理，失败时静默无提示，现在补上

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

web/src/features/groups/GroupDetailColumn.tsx

@@ -119,6 +119,11 @@ export function GroupDetailColumn({ topicId, peerName, onClose, onOpenHistory }:
   // (no extra request needed) -- live-verified this reflects the real value (flipped it via
   // GroupAdminModal's own PATCH, re-fetched `/settings`, confirmed it changed), not a frozen default.
   const canInvite = isAdmin || settingsQuery.data?.governance?.member_invite === true;
+  // Same gap as `canInvite` right above (same governance toggle pattern, same root cause: the
+  // "群文件上传权限" toggle in GroupAdminModal writes `member_upload_files` but nothing ever read it
+  // back) -- `GroupFilesModal`'s upload button was unconditionally visible/clickable regardless of
+  // this setting.
+  const canUpload = isAdmin || settingsQuery.data?.governance?.member_upload_files === true;
 
   // No `version` in the request -- see updateGroupMemberSettings's own doc comment for why sending
   // one 400s every single call (this was the actual root cause of "member-settings always 400",
@@ -159,7 +164,11 @@ export function GroupDetailColumn({ topicId, peerName, onClose, onOpenHistory }:
 
   const clearHistory = async () => {
     if (!(await requestConfirm({ message: '确定清空本群的聊天记录吗？此操作仅清除本地记录，不影响其他成员。', danger: true }))) return;
-    tinode.getTopic(topicId).delMessagesAll(false);
+    try {
+      await tinode.getTopic(topicId).delMessagesAll(false);
+    } catch (err) {
+      showError(err, '清空聊天记录失败，请重试');
+    }
   };
 
   const reportAbuse = () => {
@@ -411,7 +420,7 @@ export function GroupDetailColumn({ topicId, peerName, onClose, onOpenHistory }:
       {openModal === 'announcement' ? (
         <GroupAnnouncementModal topicId={topicId} canEdit={isAdmin} onClose={() => setOpenModal(null)} />
       ) : null}
-      {openModal === 'files' ? <GroupFilesModal topicId={topicId} isAdmin={isAdmin} onClose={() => setOpenModal(null)} /> : null}
+      {openModal === 'files' ? <GroupFilesModal topicId={topicId} isAdmin={isAdmin} canUpload={canUpload} onClose={() => setOpenModal(null)} /> : null}
       {openModal === 'admin' ? <GroupAdminModal topicId={topicId} onClose={() => setOpenModal(null)} /> : null}
       {openModal === 'qrcode' ? <QRCodeModal groupTopic={topicId} onClose={() => setOpenModal(null)} /> : null}
     </aside>