Smart WoL: TCP pre-check before sending magic packet (3s timeout).
Machine status updates via SSE: online/offline tracked in DB and
broadcast to all connected browser tabs in real-time.
- Pre-check: if machine already reachable, skip WoL and mark online
- WoL path: send 3 magic packets, wait for SSH, mark online/offline
- Backend: setMachineStatus() helper + machine_status SSE event
- Frontend: subscribeMachineStatus() SSE helper for Machines + Dashboard
- IsReachable() helper in wol package for TCP reachability checks
Fix Wake-on-LAN: set SO_BROADCAST on UDP socket, send 3 magic packets,
expose broadcast_addr and wake timeout fields in UI, add Test Wake endpoint,
surface send errors in job status, bump default wake timeout to 180s.