#13228: Add WeCom (WeChat Work / 企业微信) Channel plugin for China enterprise ecosystem

This PR introduces a production-ready WeCom (WeChat Work / 企业微信) Channel plugin for OpenClaw, enabling support for the most important enterprise messaging ecosystem in China. The plugin has gone through multiple iterations and has been validated in real-world enterprise deployments. It is now stable and feature-complete for common enterprise scenarios, including conversations, message delivery, and file handling. This significantly improves OpenClaw adoption in the China enterprise market. This solution has also been adopted and validated in public deployment guides by major cloud platforms, including Tencent Cloud, Volcengine, and CTYun, demonstrating strong stability and reproducibility. NPM Package: https://www.npmjs.com/package/@yanhaidao/wecom GitHUB: https://github.com/YanHaidao/wecom Maintainer / Author: YanHaidao (GitHub: YanHaidao) I will continue long-term maintenance and provide full implementation code as well as prompt/spec documentation to ensure reproducibility and reduce maintenance cost for upstream. 本 PR 为 OpenClaw 新增了一个生产可用的 企业微信（WeCom / WeChat Work）Channel 插件，用于支持中国最重要的企业沟通与业务协作生态。 该插件已经经历多个版本迭代，并在真实企业场景中稳定运行，目前功能较为完善，可覆盖企业常见的对话、推送、文件交付等需求，能够显著提升 OpenClaw 在中国市场的落地能力。 同时，该方案已被 腾讯云、火山引擎（Volcengine）、天翼云 等云主机/云平台的公开部署文档采用并验证，具备较强的稳定性与可复现性。 NPM 包地址： https://www.npmjs.com/package/@yanhaidao/wecom GitHUB: https://github.com/YanHaidao/wecom 维护者 / 作者：YanHaidao（GitHub: YanHaidao） 我将持续长期维护该插件，并提供完整实现代码以及对应的 Prompt / Spec 文档，降低官方后续维护成本，便于社区复现与共建。