feat: Phase 5.2 - 实现 query 处理逻辑

- 创建可取消的 context 并存储 cancel func
- 获取对话历史并传递给 orchestrator
- 启动 orchestrator.ProcessQuery goroutine 处理查询
- 请求完成后自动清理 cancel func 和活跃请求标记

backend/internal/ws/handler.go

@@ -170,19 +170,43 @@ func serveWS(c *gin.Context, sessionMgr session.Manager, orch orchestrator.Orche
 			logger.Log.Infow("query received", "session", sessionID, "request", msg.RequestID)
 
 			// 刷新会话 TTL
-			if err := sessionMgr.Touch(context.Background(), sessionID); err != nil {
+			if err := client.sessionMgr.Touch(context.Background(), sessionID); err != nil {
 				logger.Log.Warnw("touch session failed", "session", sessionID, "error", err)
 			}
 
 			// 标记活跃请求
-			if err := sessionMgr.SetActiveRequest(context.Background(), sessionID, msg.RequestID); err != nil {
+			if err := client.sessionMgr.SetActiveRequest(context.Background(), sessionID, msg.RequestID); err != nil {
 				logger.Log.Warnw("set active request failed", "session", sessionID, "error", err)
 			}
 
-			// 获取对话历史（供后续 Orchestrator 使用）
-			_, _ = sessionMgr.GetHistory(context.Background(), sessionID, 20)
+			// 获取对话历史
+			history, _ := client.sessionMgr.GetHistory(context.Background(), sessionID, 20)
 
-			// TODO: 解码 audio Base64 → 启动 orchestrator.ProcessQuery goroutine
+			// 创建可取消的 context
+			ctx, cancel := context.WithCancel(context.Background())
+			client.mu.Lock()
+			client.cancelFuncs[msg.RequestID] = cancel
+			client.mu.Unlock()
+
+			// 创建 sender
+			sender := &WSClient{client: client, requestID: msg.RequestID}
+
+			// 启动 orchestrator 处理 goroutine
+			go func() {
+				defer func() {
+					// 清理 cancel func
+					client.mu.Lock()
+					delete(client.cancelFuncs, msg.RequestID)
+					client.mu.Unlock()
+					cancel()
+					// 清除活跃请求
+					_ = client.sessionMgr.ClearActiveRequest(context.Background(), sessionID)
+				}()
+
+				if err := client.orchestrator.ProcessQuery(ctx, sessionID, msg, history, sender); err != nil {
+					logger.Log.Errorw("process query failed", "session", sessionID, "request", msg.RequestID, "error", err)
+				}
+			}()
 
 		case "config":
 			var msg models.WsConfig