fix(control): 视频源统计更新到 registry 当前设备对象

discovery 每轮会替换设备指针，graph 轮询更新旧指针导致
UI 拿到新指针(统计恒 0)。改为按 device_id 更新 registry
中当前对象。

control/internal/service/registry.go

@@ -96,17 +96,23 @@ func (s *RegistryService) startGraphPolling() {
 
         for _, dev := range onlineDevices {
             data, _, err := s.agent.Do("GET", dev.IP, dev.AgentPort, "/v1/graphs", nil)
-            if err == nil {
-                var graphs interface{}
-                if err := json.Unmarshal(data, &graphs); err == nil {
-                    s.mu.Lock()
-                    dev.Graphs = graphs
-                    total, online, down := parseVideoSourceStats(graphs)
-                    dev.VideoSourceTotal, dev.VideoSourceOnline, dev.VideoSourceDown = total, online, down
-                    s.mu.Unlock()
-                    s.persistDevice(dev)
-                }
+            if err != nil {
+                continue
             }
+            var graphs interface{}
+            if err := json.Unmarshal(data, &graphs); err != nil {
+                continue
+            }
+            total, online, down := parseVideoSourceStats(graphs)
+            s.mu.Lock()
+            // discovery 可能已替换设备指针，更新 registry 中当前对象
+            if cur, ok := s.devices[dev.DeviceID]; ok {
+                cur.Graphs = graphs
+                cur.VideoSourceTotal = total
+                cur.VideoSourceOnline = online
+                cur.VideoSourceDown = down
+            }
+            s.mu.Unlock()
         }
     }
 }