Connection confirmation race conditions prevented

When users of n8n's computer use feature receive an incoming connection request, the system displays a confirmation prompt asking whether to approve or deny the connection. A bug existed where multiple concurrent requests could trigger overlapping confirmation dialogs, creating a confusing user experience and potential race conditions.

This fix introduces a state flag that tracks whether a confirmation prompt is currently active. While that flag is true, any incoming connection requests receive an immediate 409 response with an error message. The flag is set before the confirmation prompt appears and cleared once the user responds, whether approved or denied.

The change lives in the computer use daemon, which manages the connection lifecycle between the user's machine and external services. By rejecting concurrent connection attempts, the system maintains a clean, predictable flow — users see one prompt, respond, and only then can new requests trigger another prompt.

This resolves the issue identified in NODE-4828, where multiple simultaneous confirmation prompts could leave the system in an inconsistent state.