Feat: 实现知识图谱数据库的检索方法，并对外提供接口

backend/handlers/graph_handler.go

@@ -8,22 +8,22 @@ import (
 )
 
 type GraphHandler struct {
-	dataService *services.DataService
+	service services.GraphService
 }
 
-func NewGraphHandler(dataService *services.DataService) *GraphHandler {
+func NewGraphHandler(service services.GraphService) *GraphHandler {
 	return &GraphHandler{
-		dataService: dataService,
+		service: service,
 	}
 }
 
 func (h *GraphHandler) GetGraphData(c *gin.Context) {
-	data := h.dataService.GetGraphData()
+	data := h.service.GetGraphData()
 	c.JSON(http.StatusOK, data)
 }
 
 func (h *GraphHandler) GetStats(c *gin.Context) {
-	stats := h.dataService.GetStats()
+	stats := h.service.GetStats()
 	c.JSON(http.StatusOK, gin.H{
 		"stats": stats,
 		"timestamp": gin.H{