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_

Start by reproducing the permission prompt with the listed copilot-cli steps, then trace the subagent permission approval flow. Done means the prompt shows the full command, the agent identity, relevant reasoning or context, and the actual directory scope instead of only "/".

由索引模型根據 Issue 內容生成。