refactor(backend): 优化API文档、认证路由和分页查询，统一响应格式并添加字段验证

.codebuddy/analysis-summary.json

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+{"title":"牛只交易平台后端API全面重构","features":["响应格式标准化","字段命名一致性","参数验证完善","错误处理规范化","性能优化","API测试覆盖"],"tech":{"Backend":{"language":"JavaScript","framework":"Node.js + Express.js","orm":"Sequelize","validation":"express-validator","middleware":"自定义响应格式和字段转换","testing":"Jest + Supertest"}},"design":"不涉及UI设计","plan":{"创建统一响应格式中间件，标准化为{success, data, message}格式":"done","实现字段命名转换中间件，自动处理snake_case与camelCase转换":"done","为所有API接口添加参数验证和必填项检查":"done","统一错误处理机制，创建标准错误码和错误消息":"done","优化数据库查询性能，检查Sequelize查询效率":"done","验证所有API路由路径与前端调用的一致性":"done","编写API接口测试用例，确保重构后功能正常":"done","运行集成测试验证重构结果":"done"}}