refactor: 重构neo4j服务

backend/internal/handler/search_handler.go

@@ -4,6 +4,7 @@ import (
 	"net/http"
 
 	"github.com/gin-gonic/gin"
+	"knowledge-graph-backend/internal/model"
 	"knowledge-graph-backend/internal/service"
 )
 
@@ -28,10 +29,7 @@ func NewSearchHandler(svc service.GraphService) *SearchHandler {
 func (h *SearchHandler) SearchNodes(c *gin.Context) {
 	query := c.Query("q")
 	if query == "" {
-		c.JSON(http.StatusBadRequest, gin.H{
-			"error":   "Bad Request",
-			"message": "Query parameter 'q' is required",
-		})
+		c.JSON(http.StatusBadRequest, model.ErrorResponse{Error: "bad_request", Message: "Query parameter 'q' is required"})
 		return
 	}