Fix connection logs: add background status.log sync task

ConnLogs were never populated because AppendConnLog was never called.
Added StartStatusSync() goroutine that runs every 10 seconds:

1. Iterates all running instances
2. Reads status.log via ParseStatus (status-version 3)
3. For each CLIENT_LIST entry:
   - If no active ConnLog exists → AppendConnLog (new connection)
   - If active ConnLog exists → UpdateActiveConnStats (traffic)
4. For active ConnLogs with no matching CLIENT_LIST → CloseActiveConn

Store additions:
  ListActiveConns(instanceID)  — returns all unclosed connections
  UpdateActiveConnStats()      — updates bytes in/out without flush

StartStatusSync is called from main.go right after Service creation.
UpdateActiveConnStats deliberately skips flush() to avoid writing
db.json every 10 seconds; stats are persisted on disconnect.

backend/internal/service/service.go

@@ -36,6 +36,59 @@ func New(cfg *config.Config, st *store.Store, ovm *openvpn.Manager) *Service {
 	return &Service{Cfg: cfg, Store: st, Ovm: ovm}
 }
 
+// StartStatusSync 启动后台定时任务，每 10 秒读取所有实例的 status.log，
+// 解析 CLIENT_LIST 并同步到 ConnLogs。应在 main.go 中以 goroutine 启动。
+func (s *Service) StartStatusSync() {
+	go func() {
+		ticker := time.NewTicker(10 * time.Second)
+		defer ticker.Stop()
+		for range ticker.C {
+			s.syncAllInstanceStatus()
+		}
+	}()
+}
+
+func (s *Service) syncAllInstanceStatus() {
+	instances := s.Store.ListInstances()
+	for _, in := range instances {
+		if in.Status != "running" {
+			continue
+		}
+		statusPath := filepath.Join(s.Cfg.InstanceDir(in.Name), "status.log")
+		entries, err := s.Ovm.ParseStatus(statusPath)
+		if err != nil {
+			continue // 文件不存在或解析失败,跳过
+		}
+		// 构建当前在线 CN 集合
+		onlineCNs := map[string]bool{}
+		for _, e := range entries {
+			onlineCNs[e.CommonName] = true
+			// 如果没有活跃连接记录,则新建
+			if s.Store.FindActiveConn(in.ID, e.CommonName) == nil {
+				_ = s.Store.AppendConnLog(model.ConnectionLog{
+					InstanceID:  in.ID,
+					CommonName:  e.CommonName,
+					RealIP:      e.RealAddress,
+					VPNIP:       e.VPNAddress,
+					BytesIn:     e.BytesRecv,
+					BytesOut:    e.BytesSent,
+					ConnectedAt: e.ConnectedAt,
+				})
+			} else {
+				// 更新流量统计
+				_ = s.Store.UpdateActiveConnStats(in.ID, e.CommonName, e.BytesRecv, e.BytesSent)
+			}
+		}
+		// 标记已断开的连接
+		for _, c := range s.Store.ListActiveConns(in.ID) {
+			if !onlineCNs[c.CommonName] {
+				now := time.Now()
+				_ = s.Store.CloseActiveConn(in.ID, c.CommonName, now)
+			}
+		}
+	}
+}
+
 func (s *Service) audit(c context.Context, action, target, detail, result, ip string) {
 	username, _ := c.Value("user").(string)
 	if username == "" {

backend/internal/store/store.go

@@ -287,6 +287,35 @@ func (s *Store) CloseActiveConn(instanceID, commonName string, at time.Time) err
 	return nil
 }
 
+// ListActiveConns 返回指定实例所有未断开的连接。
+func (s *Store) ListActiveConns(instanceID string) []model.ConnectionLog {
+	s.mu.RLock()
+	defer s.mu.RUnlock()
+	var out []model.ConnectionLog
+	for i := len(s.data.ConnLogs) - 1; i >= 0; i-- {
+		c := s.data.ConnLogs[i]
+		if c.InstanceID == instanceID && c.DisconnectedAt == nil {
+			out = append(out, c)
+		}
+	}
+	return out
+}
+
+// UpdateActiveConnStats 更新活跃连接的流量统计。
+func (s *Store) UpdateActiveConnStats(instanceID, commonName string, bytesIn, bytesOut int64) error {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+	for i := len(s.data.ConnLogs) - 1; i >= 0; i-- {
+		c := &s.data.ConnLogs[i]
+		if c.InstanceID == instanceID && c.CommonName == commonName && c.DisconnectedAt == nil {
+			c.BytesIn = bytesIn
+			c.BytesOut = bytesOut
+			return nil // 不 flush,避免高频写盘
+		}
+	}
+	return nil
+}
+
 // ---- Backups ----
 
 func (s *Store) ListBackups() []model.Backup {