Implement a remote method startWorker(name) in src/worker/Manager.mjs.

Requirements:

1. Check: If the worker (e.g., 'canvas') is already active, return success immediately.
2. Create: If not, use the existing createWorker and configuration injection logic to start it.
3. Handshake: Ensure the new worker is fully connected (message channels established) before returning.
4. Expose: Add startWorker to the remote config so the App worker can call it.