feat(cron): add automatic log cleanup with retention policy

Implement LogCleaner cron job to automatically clean up old log records
based on configurable retention period and maximum record count.

- Add LogCleaner with retention_days and max_records configuration
- Add EZ_LOG_RETENTION_DAYS and EZ_LOG_MAX_RECORDS environment variables
- Default to 30 days retention and 1,000,000 max records
- Include unit tests for log cleaner functionality

cmd/server/main.go

@@ -107,6 +107,10 @@ func main() {
 	quotaCtx, cancelQuota := context.WithCancel(context.Background())
 	defer cancelQuota()
 	go quotaResetter.Start(quotaCtx)
+	logCleaner := cron.NewLogCleaner(db, rdb, cfg.Log.RetentionDays, int64(cfg.Log.MaxRecords), time.Hour)
+	cleanerCtx, cancelCleaner := context.WithCancel(context.Background())
+	defer cancelCleaner()
+	go logCleaner.Start(cleanerCtx)
 
 	adminService, err := service.NewAdminService()
 	if err != nil {