安装 gstack skills 供 Cloud Agent 全局使用

## 背景
用户要求在 AskPanda 仓库安装 [gstack](https://github.com/garrytan/gstack)，并确保后续所有 Cloud Agent 都能调用其 skills。

## 验收标准
- [ ] gstack 安装脚本可在 Cloud Agent VM 上成功执行
- [ ] skills 出现在 `.cursor/skills/` 供 agent 按需加载
- [ ] AGENTS.md / hooks 确保新 agent 会话自动安装或校验
- [ ] 单元测试覆盖安装脚本关键逻辑

Start by examining the repository's existing AGENTS.md, hooks, .cursor/skills/ layout, and test setup. Run the current tests before determining where Cloud Agent installation and validation belong. Done means the gstack installer works in the Cloud Agent VM, skills are available under .cursor/skills/, new sessions install or verify them, and key installer logic has unit-test coverage.

Written by the indexing model from the issue text.