feat(ws): 在线状态管理（Redis SET + TTL 心跳续期）

- app/ws/online_service.go: 上线/下线/心跳续期/批量查询在线状态
- 集成到 WebSocket handler: 连接时写入 Redis, 断线时清除
- client.go: 添加 DisconnectHandler 回调
- Redis 键: echo:user:online (SET) + echo:user:status:{uid} (TTL 60s)

Made-with: Cursor

backend/go-service/app/ws/provider.go

@@ -19,14 +19,20 @@ func ProvidePubSub(rdb *redis.Client, hub *ws.Hub) *ws.PubSub {
 	return ws.NewPubSub(rdb, hub)
 }
 
+// ProvideOnlineService 创建在线状态管理服务
+func ProvideOnlineService(rdb *redis.Client, hub *ws.Hub, pubsub *ws.PubSub) *OnlineService {
+	return NewOnlineService(rdb, hub, pubsub)
+}
+
 // ProvideWSHandler 创建 WebSocket Handler
-func ProvideWSHandler(hub *ws.Hub, pubsub *ws.PubSub, cfg *config.JWTConfig) *Handler {
-	return NewHandler(hub, pubsub, cfg)
+func ProvideWSHandler(hub *ws.Hub, pubsub *ws.PubSub, cfg *config.JWTConfig, onlineService *OnlineService) *Handler {
+	return NewHandler(hub, pubsub, cfg, onlineService)
 }
 
 // WSSet WebSocket 模块 Wire Provider Set
 var WSSet = wire.NewSet(
 	ProvideHub,
 	ProvidePubSub,
+	ProvideOnlineService,
 	ProvideWSHandler,
 )