Fix MachineResponse: expose last_seen_at/created_at, clean status string

The status field was being decorated with "(last seen ...)" suffix
which broke frontend statusVariant() matching and prevented the
LastSeen column from showing the separate timestamp.

Changes:
- machineToResp() now returns clean status ("online"/"offline")
- MachineResponse includes last_seen_at and created_at as separate fields
- Fix whitespace typo in WakeCheckIntervalSeconds field

internal/api/handlers_machines.go

@@ -444,11 +444,10 @@ func (h *MachineHandler) Delete(w http.ResponseWriter, r *http.Request) {
 }
 
 func machineToResp(m models.Machine) MachineResponse {
-	var status string
+	var lastSeen *string
 	if m.LastSeenAt != nil {
-		status = m.Status + " (last seen " + m.LastSeenAt.Format(time.RFC3339) + ")"
-	} else {
-		status = m.Status
+		s := m.LastSeenAt.Format(time.RFC3339)
+		lastSeen = &s
 	}
 	return MachineResponse{
 		ID:                          m.ID,
@@ -461,10 +460,12 @@ func machineToResp(m models.Machine) MachineResponse {
 		WoLEnabled:                  m.WoLEnabled,
 		BroadcastAddr:               m.BroadcastAddr,
 		WakeTimeoutSeconds:          m.WakeTimeoutSeconds,
-		WakeCheckIntervalSeconds:     m.WakeCheckIntervalSeconds,
+		WakeCheckIntervalSeconds:    m.WakeCheckIntervalSeconds,
 		FingerprintConfirmed:        m.FingerprintConfirmed,
-		HostKeyFingerprint:         m.HostKeyFingerprint,
-		Status:                      status,
+		HostKeyFingerprint:          m.HostKeyFingerprint,
+		Status:                      m.Status,
+		LastSeenAt:                  lastSeen,
+		CreatedAt:                   m.CreatedAt.Format(time.RFC3339),
 	}
 }