feat: 统一全局 Header 结构

- 新增 AppHeader 组件（Logo + 台入口 + 用户状态）
- 新增 UserDropdown 组件（用户下拉菜单）
- 新增 AppLayout 布局组件
- 移除 SidebarBrand 和 SidebarUser 组件
- 修改各台页面，移除侧边栏中的品牌区和用户区
- 修改 HomePage，移除独立 header/footer
- 修改 Layout 组件，简化为 sidebar + content
- 账户设置改为弹框形式，不中断用户操作
- 更新 README.md 布局系统说明
- 同步 delta specs 到主 specs

src/pages/AdminPage.jsx

@@ -2,8 +2,6 @@ import { useState, useEffect } from 'react';
 import { useLocation, useNavigate } from 'react-router-dom';
 import { FiHome, FiBarChart2, FiUsers, FiList, FiCheckCircle, FiActivity, FiSettings } from 'react-icons/fi';
 import Layout from '../components/Layout.jsx';
-import SidebarBrand from '../components/layout/SidebarBrand.jsx';
-import SidebarUser from '../components/layout/SidebarUser.jsx';
 import SidebarNavItem from '../components/layout/SidebarNavItem.jsx';
 import usePageState from '../hooks/usePageState.js';
 import { ADMIN_PAGES } from '../constants/pages.js';
@@ -20,7 +18,6 @@ import ConsoleReviewListPage from './console/ConsoleReviewListPage.jsx';
 import ConsoleReviewDetailPage from './console/ConsoleReviewDetailPage.jsx';
 import ModelConfigsPage from './admin/ModelConfigsPage.jsx';
 import AddModelConfigPage from './admin/AddModelConfigPage.jsx';
-import AccountPage from '../components/account/AccountPage.jsx';
 
 function AdminPage() {
     const location = useLocation();
@@ -107,30 +104,13 @@ function AdminPage() {
                     onBack={() => navigateTo('modelConfigs')}
                     editData={editData}
                 />;
-            case 'account':
-                return <AccountPage />;
             default:
                 return <div>Page not found</div>;
         }
     };
 
-    const getPageTitle = () => {
-        if (editData && (currentPage === 'addDepartment' || currentPage === 'addUser' || currentPage === 'addProject' || currentPage === 'addModelConfig')) {
-            const prefix = '编辑';
-            const nameMap = { addDepartment: '部门', addUser: '用户', addProject: '项目', addModelConfig: '配置' };
-            return prefix + nameMap[currentPage];
-        }
-        if (currentPage === 'reviewDetail') {
-            return reviewType === 'version' ? '版本审核' : '下架审核';
-        }
-        return ADMIN_PAGES[currentPage]?.title || '';
-    };
-
     const sidebar = (
         <>
-            <div className="admin-sidebar-header">
-                <SidebarBrand subtitle="运营管理台" />
-            </div>
             <nav className="admin-sidebar-nav">
                 <SidebarNavItem
                     icon={<FiHome />}
@@ -196,20 +176,12 @@ function AdminPage() {
                     textClassName="admin-nav-text"
                 />
             </nav>
-            <SidebarUser
-                onClick={() => navigateTo('account')}
-                wrapperClassName="admin-sidebar-user"
-                infoClassName="admin-sidebar-user-info"
-                nameClassName="admin-sidebar-user-name"
-                roleClassName="admin-sidebar-user-role"
-            />
         </>
     );
 
     return (
         <Layout
             sidebar={sidebar}
-            headerTitle={getPageTitle()}
             sidebarClassName="admin-sidebar"
         >
             {renderPage()}