- Create DiscoveryWorker for handling SNMP device discovery
- Replace Task.start with Exq.enqueue for discovery operations
- Enqueue jobs to 'discovery' queue with device_id parameter
- Add enqueue_discovery/1 helper that falls back to Task.start in test
- Discovery jobs now persistent and retryable via Exq
- Triggered on: new device creation, device update, manual rediscover button