Fix path separator for remote_zip in computer_client.py

[tjc6666666666666]

Ensure remote_zip uses forward slashes for compatibility.

Modifications / 改动点

• This is NOT a breaking change. / 这不是一个破坏性变更。

Screenshots or Test Results / 运行截图或测试结果

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Checklist / 检查清单

• 😊 If there are new features added in the PR, I have discussed it with the authors through issues/emails, etc.
  / 如果 PR 中有新加入的功能，已经通过 Issue / 邮件等方式和作者讨论过。

• 👀 My changes have been well-tested, and "Verification Steps" and "Screenshots" have been provided above.
  / 我的更改经过了良好的测试，并已在上方提供了“验证步骤”和“运行截图”。

• 🤓 I have ensured that no new dependencies are introduced, OR if new dependencies are introduced, they have been added to the appropriate locations in requirements.txt and pyproject.toml.
  / 我确保没有引入新依赖库，或者引入了新依赖库的同时将其添加到 requirements.txt 和 pyproject.toml 文件相应位置。

• 😮 My changes do not introduce malicious code.
  / 我的更改没有引入恶意代码。

Summary by Sourcery

Bug Fixes:

• Fix incorrect path separator when constructing the remote skills.zip path for sandbox uploads.

[sourcery-ai]

Hey - I've left some high level feedback:

• To avoid potential // in the path if SANDBOX_SKILLS_ROOT already ends with a slash, consider normalizing it, e.g., remote_zip = f"{SANDBOX_SKILLS_ROOT.rstrip('/')}/skills.zip".
• Since this path is intended to be POSIX-style, it may be clearer and more robust to construct it via PurePosixPath (or a small helper) instead of manual string concatenation so that future call sites remain consistent.

Prompt for AI Agents

Please address the comments from this code review:

## Overall Comments
- To avoid potential `//` in the path if `SANDBOX_SKILLS_ROOT` already ends with a slash, consider normalizing it, e.g., `remote_zip = f"{SANDBOX_SKILLS_ROOT.rstrip('/')}/skills.zip"`.
- Since this path is intended to be POSIX-style, it may be clearer and more robust to construct it via `PurePosixPath` (or a small helper) instead of manual string concatenation so that future call sites remain consistent.

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[gemini-code-assist]

Code Review

This pull request modifies the path construction for the sandbox skills bundle in computer_client.py to ensure forward slashes are used for compatibility. The reviewer suggests using the more idiomatic Path.as_posix() method instead of manual string concatenation and recommends translating the Chinese comment into English to maintain consistency with the rest of the codebase.