♻️ refactor(admin): 移除管理后台的主题提供器

- 删除ThemeProvider组件，简化应用结构
- 移除默认主题设置和主题存储相关代码

src/client/admin-shadcn/index.tsx

@@ -1,7 +1,6 @@
 import { createRoot } from 'react-dom/client'
 import { RouterProvider } from 'react-router';
 import { QueryClient, QueryClientProvider } from '@tanstack/react-query';
-import { ThemeProvider } from '@/client/components/theme-provider';
 import { Toaster } from '@/client/components/ui/sonner';
 import dayjs from 'dayjs';
 import weekday from 'dayjs/plugin/weekday';
@@ -32,17 +31,15 @@ const queryClient = new QueryClient({
 const App = () => {
   return (
     <QueryClientProvider client={queryClient}>
-      <ThemeProvider defaultTheme="light" storageKey="admin-theme">
-        <AuthProvider>
-          <RouterProvider router={router} />
-          <Toaster 
-            position="top-right"
-            expand={false}
-            richColors
-            closeButton
-          />
-        </AuthProvider>
-      </ThemeProvider>
+      <AuthProvider>
+        <RouterProvider router={router} />
+        <Toaster 
+          position="top-right"
+          expand={false}
+          richColors
+          closeButton
+        />
+      </AuthProvider>
     </QueryClientProvider>
   )
 };