feat: 更新 Server 后端服务

- 更新 agent handler 和 service 层
- 新增 chat_group handler 和 service
- 删除废弃的 chat_handler
- 更新 tool 相关处理
- 更新 API 文档和依赖

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

server/internal/handler/chat_group_handler.go

@@ -1,6 +1,7 @@
 package handler
 
 import (
+	"log"
 	"net/http"
 	"strconv"
 
@@ -140,10 +141,13 @@ func (h *ChatGroupHandler) GroupChat(c *gin.Context) {
 	}
 
 	response, err := h.groupService.GroupChat(userID, req.Message, agentIDs, req.SessionID)
+	log.Printf("[ChatGroupHandler] Got response, err: %v", err)
 	if err != nil {
 		c.JSON(http.StatusInternalServerError, gin.H{"error": err.Error()})
 		return
 	}
 
+	log.Printf("[ChatGroupHandler] Response subtask_results: %+v", response.SubtaskResults)
+
 	c.JSON(http.StatusOK, response)
 }