subagent permission approval lacks context and is confusing

### Describe the bug

Linux subagents can run commands that the permission pattern only captures "/" as the directory which is super dangerous, without giving me the exact command will be run and context around it like a regular agent.

### Affected version

_No response_

### Steps to reproduce the behavior

1. run copilot-cli
2. ask it to run a command in subagent that require additional permission
3. find that permission itself got prompted, but reasoning/context isn't

### Expected behavior

I should be able to see which agent and its full glory

### Additional context

_No response_

首先按照列出的 copilot-cli 步骤复现权限提示，然后跟踪 subagent 的权限审批流程。完成的标准是：提示中显示完整命令、agent 身份、相关推理或上下文，以及实际的目录范围，而不是仅显示 "/"。

由索引模型根据 Issue 内容生成。