add MemOS plugin one-click install skill (#1394)

## Description

fix: Clarify missing prerequisites and minor inaccuracies in MemOS
OpenClaw local plugin installation guidance.
feat: Add SKILL.md for one-click installation of the MemOS (OpenClaw
local) plugin.

## Type of change

- [ ] Bug fix (non-breaking change which fixes an issue)
- [x] New feature (non-breaking change which adds functionality)

## How Has This Been Tested?

- [x] Manual verification - followed
`apps/memos-local-openclaw/site/public/SKILL.md` and confirmed the
plugin install flow end-to-end

## Checklist

- [x] I have performed a self-review of my own code | 我已自行检查了自己的代码
- [x] I have commented my code in hard-to-understand areas |
我已在难以理解的地方对代码进行了注释
- [x] I have added tests that prove my fix is effective or that my
feature works | 我已添加测试以证明我的修复有效或功能正常
- [ ] I have created related documentation issue/PR in
[MemOS-Docs](https://github.com/MemTensor/MemOS-Docs) (if applicable) |
我已在 [MemOS-Docs](https://github.com/MemTensor/MemOS-Docs) 中创建了相关的文档
issue/PR（如果适用）
- [ ] I have linked the issue to this PR (if applicable) | 我已将 issue
链接到此 PR（如果适用）
- [ ] I have mentioned the person who will review this PR | 我已提及将审查此 PR
的人

## Reviewer Checklist
- [ ] closes #xxxx (Replace xxxx with the GitHub issue number)
- [ ] Made sure Checks passed
- [ ] Tests have been provided

Author: CaralHsi