[FEATURE] Notification hooks for Claude Desktop app (e.g., Slack/OS notification on turn completion)

The Claude Desktop app currently has no way to notify the user when a turn/response is complete. Claude Code (CLI) has excellent support for this via Notification hooks with the idle_prompt matcher, but the Desktop app lacks any equivalent.

Use case

When running long responses, I'd like to get notified (via Slack, OS notification, or other channels) when Claude finishes, rather than having to keep checking the window.

Suggestion

Expose lifecycle events (like turn completion) in the Desktop app, similar to Claude Code's hook system, so users can configure custom notifications.