- Remove standard log import from server_metrics.go
- Add logrus import for structured logging
- Replace log.Printf with logrus.WithError for system metrics storage errors
- Replace log.Printf with logrus.WithError for subscriber count errors (total, active, suspended)
- Replace log.Printf with logrus.WithError for active sessions count errors
- Replace log.Printf with logrus.WithError for /proc/stat, /proc/meminfo, and /proc/net/dev read errors