feat: 全链路追踪增强 + 超时修复

- ethend /api/trace/recent: 新增消息收发事件(platform-bridge日志)
- 消息按管线聚合: msg_received → llm_call → tool_call → msg_sent
- platform-bridge→ai-core超时 120s→180s

Co-Authored-By: Claude <noreply@anthropic.com>

backend/platform-bridge/cmd/main.go

@@ -696,7 +696,7 @@ func forwardToAICore(cfg *config.Config, msg *bridge.UnifiedMessage, mode, userI
 		req.Header.Set("X-Internal-Token", cfg.InternalToken)
 	}
 
-	client := &http.Client{Timeout: 120 * time.Second}
+	client := &http.Client{Timeout: 180 * time.Second}
 	resp, err := client.Do(req)
 	if err != nil {
 		return nil, fmt.Errorf("forward to ai-core failed: %w", err)