实现对话记录页并对齐工作台三栏布局

完善会话列表筛选与摘要字段、归档接口；对话记录按效果图重构；工作台顶栏等高对齐；默认管理员账号改为 kefu_admin / kefu_admin123。

web/src/pages/Login.tsx

@@ -35,10 +35,10 @@ const Login = () => {
         </div>
         <Form form={form} layout="vertical" onFinish={onFinish} autoComplete="off">
           <Form.Item name="username" label="用户名" rules={[{ required: true, message: '请输入用户名' }]}>
-            <Input placeholder="admin / agent1" size="large" />
+            <Input placeholder="kefu_admin" size="large" />
           </Form.Item>
           <Form.Item name="password" label="密码" rules={[{ required: true, message: '请输入密码' }]}>
-            <Input.Password placeholder="password123" size="large" />
+            <Input.Password placeholder="kefu_admin123" size="large" />
           </Form.Item>
           <Form.Item>
             <Button type="primary" htmlType="submit" block size="large" loading={loading}>