fix(test): 修复测试环境问题

1. jest.setup.js:
   - 添加 Request/Response/Headers 全局对象 mock
   - 解决 'Request is not defined' 错误

2. .eslintrc.json:
   - 将 jest.setup.js 添加到忽略列表

3. shared-mocks.tsx:
   - 添加 ArrowUp 图标 mock

4. back-to-top.test.tsx:
   - 重写测试使用 import 语法
   - 使用 fireEvent.scroll 触发滚动事件
   - 修复组件渲染测试

src/__mocks__/shared-mocks.tsx

@@ -84,6 +84,7 @@ export const mockLucideReact = () => {
   jest.mock('lucide-react', () => ({
     ArrowRight: () => <span data-testid="arrow-right" />,
     ArrowLeft: () => <span data-testid="arrow-left" />,
+    ArrowUp: () => <span data-testid="arrow-up" />,
     Shield: () => <span data-testid="shield-icon" />,
     Zap: () => <span data-testid="zap-icon" />,
     Award: () => <span data-testid="award-icon" />,