Implements health monitoring in the agent using ICMP ping, allowing
devices assigned to local (non-cloud) agents to be monitored.
Changes:
- Add surge-ping library for async ICMP ping operations
- Create ping.rs module with ping_device() function (5s timeout)
- Rename JobType::MONITOR to JobType::PING in protobuf
- Add monitoring_check channels for result communication
- Implement execute_ping_job() to handle PING jobs
- Update TUI to display ping result events
The agent now receives PING jobs from Phoenix, executes ICMP pings,
and sends MonitoringCheck results back for storage in the database.
Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>
