feat: add tab switching to App component

- Add PageType type definition
- Add currentPage state
- Add tab switching buttons
- Add conditional rendering of pages

Co-Authored-By: Claude Op. 4.6 <noreply@anthropic.com>

entrypoints/popup/App.tsx

@@ -1,10 +1,33 @@
+import { useState } from 'react';
+import { Box, Button } from '@mui/material';
 import TimestampPage from './pages/TimestampPage';
+import StorageCleanerPage from './pages/StorageCleanerPage';
 import './App.css';
 
+type PageType = 'timestamp' | 'storageCleaner';
+
 function App() {
+  const [currentPage, setCurrentPage] = useState<PageType>('timestamp');
+
   return (
     <div className="app">
-      <TimestampPage />
+      <Box sx={{ display: 'flex', justifyContent: 'center', mb: 2 }}>
+        <Button
+          variant={currentPage === 'timestamp' ? 'contained' : 'outlined'}
+          onClick={() => setCurrentPage('timestamp')}
+        >
+          时间戳
+        </Button>
+        <Button
+          variant={currentPage === 'storageCleaner' ? 'contained' : 'outlined'}
+          onClick={() => setCurrentPage('storageCleaner')}
+          sx={{ ml: 1 }}
+        >
+          存储清理
+        </Button>
+      </Box>
+      {currentPage === 'timestamp' && <TimestampPage />}
+      {currentPage === 'storageCleaner' && <StorageCleanerPage />}
     </div>
   );
 }