fix(仪表盘): 增加对数据库驱动和仓储实例的有效性检查

backend/internal/service/dashboard_service.go

@@ -85,6 +85,9 @@ func NewDashboardService(usageRepo UsageLogRepository, aggRepo DashboardAggregat
 			aggUsageDays = cfg.DashboardAgg.Retention.UsageLogsDays
 		}
 	}
+	if aggRepo == nil {
+		aggEnabled = false
+	}
 	return &DashboardService{
 		usageRepo:      usageRepo,
 		aggRepo:        aggRepo,