fix(websocket): errors in saving client info during ping ping

backend/utils/db/ws_clients.go

@@ -12,7 +12,7 @@ type ClientRecord struct {
 	IPAddress      string    `gorm:"not null"`
 	UserAgent      string    `gorm:"size:255"`
 	ConnectedAt    time.Time `gorm:"index"`
-	LastHeartbeat  time.Time `gorm:"index"`
+	LastHeartbeat  time.Time `gorm:"column:last_heartbeat"`
 	Channels       JSONB     `gorm:"type:jsonb"`
 	CreatedAt      time.Time
 	UpdatedAt      time.Time