Add /remove-dir command to revoke directory access

首先检查现有的 /add-dir 和 /list-dirs 命令入口，以及当前会话的目录权限是如何被跟踪的。根据所要求的行为定义完成标准：从 /list-dirs 中移除、安全卸载已加载的资源、明确报告活动引用或正在运行的工作，以及对不允许的路径返回错误。

Describe the feature or problem you'd like to solve

Copilot CLI provides /add-dir and /list-dirs, but no corresponding command to remove a previously allowed directory. Users cannot reduce directory access during a session without restarting or otherwise resetting session state.

Proposed solution

Add /remove-dir <path> as the counterpart to /add-dir. It should:

• Revoke file access to the specified previously allowed directory for the current session.
• Remove the directory from /list-dirs immediately.
• Unload trusted skills, agents, and instructions loaded from that directory when safe.
• Clearly report active references or running work that prevent immediate removal.
• Return a clear error when the path is not currently allowed.

This improves least-privilege workflows by allowing users to grant temporary access and revoke it as soon as it is no longer needed, without restarting the session.

Example prompts or workflows

1. /add-dir C:\work\shared-library, work with files there, then run /remove-dir C:\work\shared-library when finished.

2. Run /list-dirs, identify an accidentally added directory, and remove it with /remove-dir <path>.

3. Temporarily allow access to generated artifacts, inspect them, then revoke access while keeping the current conversation.

4. Attempt to remove a directory used by a running task and receive a clear message explaining what must finish or stop first.

Additional context

A dedicated removal command would make /add-dir reversible and provide a clearer least-privilege permission model. /reset-allowed-tools does not address directory access, and restarting a session is unnecessarily disruptive.