v0.1.6

feat: add device online/offline status with ping check

- Add POST /api/ping endpoint with concurrent ICMP ping (up to 8 threads)
- Add pingIp field to device model for reachability checks
- Add StatusDot component with green/red/gray indicators and pulse animation
- Add 30-second auto-polling and manual refresh button in web UI
- Update fallback HTML with status column and pingIp form field
- Update README API reference
- Rewrite CHANGELOG to cover all releases