feat(analytics): 前端 ECharts CustomChart 注册 + 数据契约类型扩展

- BaseEChart 注册 CustomChart 支持区间渲染
- FlowInterval 类型扩为 6 位（含 isMain）
- FlowDevice 增加 lead_time/started_at

frontend/src/components/BaseEChart.tsx

@@ -2,7 +2,7 @@
  *  支持 onEvents（常规事件）与 onZrClick（ZRender 底层点击，扩大热区）。 */
 import { useEffect, useRef } from "react";
 import * as echarts from "echarts/core";
-import { LineChart, BarChart } from "echarts/charts";
+import { LineChart, BarChart, CustomChart } from "echarts/charts";
 import {
   GridComponent, TooltipComponent, LegendComponent, DataZoomComponent,
 } from "echarts/components";
@@ -13,6 +13,7 @@ import type { EChartsCoreOption } from "echarts/core";
 echarts.use([
   LineChart,
   BarChart,
+  CustomChart,
   GridComponent,
   TooltipComponent,
   LegendComponent,