Add an sound notification for Claude harness permission prompts

VS Code Agent mode supports switching the agent harness between Local and Claude.

When the Local harness requires approval, VS Code displays the permission prompt and plays the expected notification sound. When switching to the Claude harness, permission requests do not produce the same sound notification.

The Claude Agent SDK exposes a `permission_prompt` notification through its Notification hook. Please add equivalent VS Code support for Claude harness permission prompts, ideally behind a setting so users can enable or disable the sound.

Environment:
- OS: Linux
- Surface: VS Code Copilot Chat Agent mode
- Harness: Claude
- Expected: permission prompt produces an audible notification
- Actual: permission prompt appears without the sound notification

References:
https://docs.github.com/en/copilot/concepts/agents/anthropic-claude
https://code.claude.com/docs/en/agent-sdk/hooks