refactor: 移除 TopBar 组件，重构功能导航并引入主题切换按钮

- 删除 TopBar 及其相关组件和逻辑，简化布局结构。
- 新增 FeatureNav 组件，包含功能导航和主题切换按钮。
- 更新 README.md，反映新的组件结构和功能。
- 修改测试用例，确保新结构下的功能正常。

src/layout/FeatureNav/__tests__/index.test.tsx

@@ -2,6 +2,21 @@ import { beforeEach, describe, expect, it, vi } from 'vitest';
 import { fireEvent, render, screen } from '@testing-library/react';
 import type { PageType } from '@/types/storage';
 import FeatureNav from '@/layout/FeatureNav';
+import { ThemeModeProvider } from '@/providers/ThemeModeProvider';
+
+Object.defineProperty(window, 'matchMedia', {
+  writable: true,
+  value: vi.fn().mockImplementation((query: string) => ({
+    matches: false,
+    media: query,
+    onchange: null,
+    addListener: vi.fn(),
+    removeListener: vi.fn(),
+    addEventListener: vi.fn(),
+    removeEventListener: vi.fn(),
+    dispatchEvent: vi.fn(),
+  })),
+});
 
 const mockNavigateTo = vi.fn();
 
@@ -28,8 +43,15 @@ describe('FeatureNav 组件', () => {
     mockRouterValue.visiblePages = ['timestamp', 'jwt', 'storageCleaner'];
   });
 
+  const renderFeatureNav = () =>
+    render(
+      <ThemeModeProvider>
+        <FeatureNav />
+      </ThemeModeProvider>,
+    );
+
   it('应渲染全部可见工具图标', () => {
-    render(<FeatureNav />);
+    renderFeatureNav();
 
     expect(screen.getByLabelText('JWT 解析')).toBeInTheDocument();
     expect(screen.getByLabelText('时间戳')).toBeInTheDocument();
@@ -37,18 +59,24 @@ describe('FeatureNav 组件', () => {
   });
 
   it('点击图标应调用 navigateTo', () => {
-    render(<FeatureNav />);
+    renderFeatureNav();
 
     fireEvent.click(screen.getByLabelText('JWT 解析'));
     expect(mockNavigateTo).toHaveBeenCalledWith('jwt');
   });
 
   it('当前页对应项应有 active 样式与 aria-current', () => {
-    render(<FeatureNav />);
+    renderFeatureNav();
 
     const activeButton = screen.getByLabelText('时间戳');
     expect(activeButton).toHaveAttribute('aria-current', 'page');
     expect(activeButton).toHaveClass('bg-muted');
     expect(activeButton).toHaveClass('border-primary');
   });
+
+  it('应渲染主题切换按钮', () => {
+    renderFeatureNav();
+
+    expect(screen.getByLabelText(/切换到/)).toBeInTheDocument();
+  });
 });