Feature Request: Allow sub-agents to inherit parent permission settings

Problem

Sub-agents prompt for permissions that the parent session has already granted.

Example:

1. Parent grants permission for Bash(npm test:*)
2. Sub-agent spawns and asks for permission to run npm test again

Proposed Solution

Add a setting to inherit parent permissions:

{
  "permissions": {
    "subagentInheritance": true
  }
}

Current Workarounds

• permissionMode: bypassPermissions — too broad, skips all permissions
• permissionMode: acceptEdits — only covers file edits
• Pre-configured allow rules — doesn't cover session-granted permissions

None of these actually inherit the parent's permissions.