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

jest.setup.js

@@ -4,6 +4,51 @@ const { TextEncoder, TextDecoder } = require('util');
 global.TextEncoder = TextEncoder;
 global.TextDecoder = TextDecoder;
 
+if (typeof global.Request === 'undefined') {
+  global.Request = class Request {
+    constructor(input, init = {}) {
+      this.url = typeof input === 'string' ? input : input.url;
+      this.method = init.method || 'GET';
+      this.headers = new Map(Object.entries(init.headers || {}));
+      this.body = init.body;
+    }
+    async json() {
+      return typeof this.body === 'string' ? JSON.parse(this.body) : this.body;
+    }
+  };
+}
+
+if (typeof global.Response === 'undefined') {
+  global.Response = class Response {
+    constructor(body, init = {}) {
+      this.body = body;
+      this.status = init.status || 200;
+      this.statusText = init.statusText || 'OK';
+      this.headers = new Map(Object.entries(init.headers || {}));
+    }
+    async json() {
+      return typeof this.body === 'string' ? JSON.parse(this.body) : this.body;
+    }
+    async text() {
+      return typeof this.body === 'string' ? this.body : JSON.stringify(this.body);
+    }
+  };
+}
+
+if (typeof global.Headers === 'undefined') {
+  global.Headers = class Headers {
+    constructor(init = {}) {
+      this._headers = new Map(Object.entries(init));
+    }
+    get(name) {
+      return this._headers.get(name);
+    }
+    set(name, value) {
+      this._headers.set(name, value);
+    }
+  };
+}
+
 const { setupAllMocks } = require('./src/__mocks__/shared-mocks');
 
 setupAllMocks();