API endpoints for Bulk Agent Deployment

Essential for scale on TypingMind Custom

We're automating bulk agent deployment and have successfully reverse-engineered the training file upload workflow via /api/hosted/blobs.

However, we still need API endpoints for:

1. Setting agent visibility to specific groups

- Current: Manual toggle after JSON import

- Need: API to assign agent to group(s) programmatically

- Use case: Prevent brief "visible to all" window during deployment

2. Importing agent JSON programmatically

- Current: Manual import via UI

- Need: POST endpoint for agent creation from JSON export

- Use case: Fully automated agent deployment pipeline