Introduced a new public documentation site for client integration at `/docs` and `/docs/integration`, removing the need for admin login. Updated the integration guide to redirect from the old admin path to the new documentation site. Added localization support for the integration documentation in English, Nepali, and Chinese. Enhanced the layout structure and improved the handling of currency display in settlement bills.
更新 .env.example，提供更清晰的 API 配置说明与本地开发环境配置指引。
修改 next.config.ts：支持动态解析允许的开发环境来源（origins），提升配置灵活性。
重构 admin-language-switcher：优化语言切换同步机制，确保语言变更能够及时生效。
优化英文、尼泊尔语与中文语言包中的错误提示文案，进一步明确 API 配置要求。
精简 admin-http.ts：将 API Base URL 校验逻辑抽离至独立模块并统一导出，提升代码可维护性。
- Added AdminLanguageSwitcher to the login form for improved language selection.
- Replaced inline script with next/script component for better performance and safety in layout.tsx.
- Updated language initialization logic to ensure consistent SSR and client rendering.
