- Add /agents/{agent_id}/heartbeat endpoint to receive and process agent heartbeats
- Add /tasks/queues endpoint to retrieve task queue sizes across all priorities
- Add /tasks/queues/{priority}/clear endpoint to clear specific priority queues
- Add /tasks/queues/stats endpoint to get detailed queue and distribution statistics
- Implement get_queue_sizes() method in TaskDistributor to return queue sizes by priority
- Implement clear_queue() method in TaskDistributor to drain
