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/ConsolePage.jsx

@@ -3,8 +3,6 @@ import { useLocation, useNavigate } from 'react-router-dom';
 import { FiPlus, FiClock, FiList, FiUsers, FiBox } from 'react-icons/fi';
 import { FaPuzzlePiece } from 'react-icons/fa';
 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 { CONSOLE_PAGES } from '../constants/pages.js';
@@ -18,7 +16,6 @@ import SkillConfigPage from './console/SkillConfigPage.jsx';
 import LogsPage from './console/LogsPage.jsx';
 import TasksPage from './console/TasksPage.jsx';
 import TaskDetailPage from './console/TaskDetailPage.jsx';
-import AccountPage from '../components/account/AccountPage.jsx';
 import ProjectsPage from './console/ProjectsPage.jsx';
 import MemberConfigPage from './console/MemberConfigPage.jsx';
 import AddMemberPage from './console/AddMemberPage.jsx';
@@ -120,8 +117,6 @@ function ConsolePage() {
                     taskId={currentTaskId}
                     onBack={() => switchPage('scheduledTasks')}
                 />;
-            case 'account':
-                return <AccountPage />;
             case 'projects':
                 return <ProjectsPage onAddMember={() => switchPage('addMember')} />;
             case 'memberConfig':
@@ -149,8 +144,6 @@ function ConsolePage() {
     const sidebar = (
         <>
             <div className="chat-sidebar-header">
-                <SidebarBrand subtitle="企业级AI平台" />
-                <div className="sidebar-divider"></div>
                 <button className="btn btn-primary" style={{ width: '100%' }} onClick={createNewChat}>
                     <span style={{ display: 'flex', alignItems: 'center', justifyContent: 'center', gap: '6px' }}>
                         <FiPlus /> 新建对话
@@ -209,14 +202,12 @@ function ConsolePage() {
                     onClick={() => switchPage('projects')}
                 />
             </div>
-            <SidebarUser onClick={() => switchPage('account')} />
         </>
     );
 
     return (
         <Layout
             sidebar={sidebar}
-            headerTitle={getPageTitle()}
             sidebarClassName="chat-sidebar"
             contentClassName={currentPage === 'chat' ? 'page-content-full' : ''}
         >