refactor: 移除顶部栏，设置按钮移至底部栏右侧，StatusBar 全面改 MUI Table

- StatusBar: 全 MUI Table 布局，左侧状态/Provider/Token，右侧版本+设置
- Header: 已删除(功能合并到 StatusBar)
- App.tsx: 移除 Header 引用

src/App.tsx

@@ -9,7 +9,6 @@
 
 import { ThemeProvider, CssBaseline } from '@mui/material';
 import { useEffect } from 'react';
-import { Header } from '@renderer/components/layout/Header';
 import { Sidebar } from '@renderer/components/layout/Sidebar';
 import { DetailPanel } from '@renderer/components/layout/DetailPanel';
 import { StatusBar } from '@renderer/components/layout/StatusBar';
@@ -55,7 +54,6 @@ export default function App(): React.JSX.Element {
         className="h-screen w-screen flex flex-col overflow-hidden select-none"
         style={{ background: muiTheme.palette.background.default, color: muiTheme.palette.text.primary }}
       >
-        <Header />
         <div className="flex-1 flex overflow-hidden min-h-0">
           <Sidebar />
           <ChatPanel />