GitLab

- 添加 Accept-Language 请求头支持后端翻译
- 优化账户状态指示器和测试模态框
- 简化用户属性表单和配置模态框
- 新增多个国际化翻译条目
- 重构管理视图代码，提升可维护性

Add Vue components and API client for managing user custom attributes.

- Add userAttributes API client with CRUD operations
- Add UserAttributeForm component for displaying/editing attribute values
- Add UserAttributesConfigModal for attribute definition management
- Support all attribute types: text, textarea, number, email, url,
  date, select, multi_select

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Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>