修复群组管理页"设置群头像"按钮样式退化成浏览器默认外观

.group-governance 下所有行样式都挂在 "section > button" 选择器上，这一个按钮没包在
<section> 里，完全没吃到列表行样式（全宽/分割线/内边距），退化成一个居左的灰色圆角
小按钮。包一层 <section> 即可，其余4个链接本来就是这样。

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

src/views/group-management-view.jsx

@@ -670,7 +670,9 @@ function Governance({topic, tinode, onToast}) {
   return <div className="group-page">
     <Header title="群组管理" back="group-settings" backTopic={topic} />
     <main className="group-governance">
+      <section>
         <button type="button" onClick={() => navigate('group-avatar', topic)}><span>设置群头像</span><Icon>chevron_right</Icon></button>
+      </section>
       <section>
         <button type="button" onClick={() => navigate('group-join-requests', topic)}><span>邀请进群申请</span><Icon>chevron_right</Icon></button>
         <button type="button" onClick={() => navigate('group-muted', topic)}><span>禁言的群成员</span><Icon>chevron_right</Icon></button>

umd/index.dev.js

@@ -11944,7 +11944,8 @@ function Governance({
       backTopic: topic
     }, void 0, false), (0,react_jsx_dev_runtime__WEBPACK_IMPORTED_MODULE_6__.jsxDEV)("main", {
       className: "group-governance",
-      children: [(0,react_jsx_dev_runtime__WEBPACK_IMPORTED_MODULE_6__.jsxDEV)("button", {
+      children: [(0,react_jsx_dev_runtime__WEBPACK_IMPORTED_MODULE_6__.jsxDEV)("section", {
+        children: (0,react_jsx_dev_runtime__WEBPACK_IMPORTED_MODULE_6__.jsxDEV)("button", {
           type: "button",
           onClick: () => navigate('group-avatar', topic),
           children: [(0,react_jsx_dev_runtime__WEBPACK_IMPORTED_MODULE_6__.jsxDEV)("span", {
@@ -11952,7 +11953,8 @@ function Governance({
           }, void 0, false), (0,react_jsx_dev_runtime__WEBPACK_IMPORTED_MODULE_6__.jsxDEV)(Icon, {
             children: "chevron_right"
           }, void 0, false)]
-      }, void 0, true), (0,react_jsx_dev_runtime__WEBPACK_IMPORTED_MODULE_6__.jsxDEV)("section", {
+        }, void 0, true)
+      }, void 0, false), (0,react_jsx_dev_runtime__WEBPACK_IMPORTED_MODULE_6__.jsxDEV)("section", {
         children: [(0,react_jsx_dev_runtime__WEBPACK_IMPORTED_MODULE_6__.jsxDEV)("button", {
           type: "button",
           onClick: () => navigate('group-join-requests', topic),