Refactor financial chart implementation

js/charts/ppmt_margins.js

@@ -1,6 +1,6 @@
 import { col } from '../csv.js';
 import {
-  PALETTE, FONT, axisCommon, periodAxis, titleStyle, legendStyle,
+  PALETTE, FONT, axisCommon, periodAxis, titleStyle, standardLegend,
   lineSeries, footnote, watermarks, LAYOUT,
 } from '../theme.js';
 
@@ -64,18 +64,7 @@ export function ppmtMarginsChart(rows, { width, height }) {
       text: '泡泡玛特利润率与费用率拆解（2020H1-2026H1）',
       subtext: '毛利率抬升叠加费用率下降，共同推动净利率走高（H1为半年，H2为全年累计）',
     },
-    legend: {
-      // 不继承 legendStyle：它带 icon:'roundRect'，会盖掉 ECharts 按系列
-      // 自动生成的「短线+空心圆」图例
-      top: LAYOUT.legendTop,
-      itemGap: 28,
-      textStyle: {
-        color: PALETTE.ink,
-        fontSize: 14,
-        fontFamily: FONT,
-      },
-      data: SERIES.map((s) => s.name),
-    },
+    legend: standardLegend(SERIES.map((series) => series.name)),
     grid: { left: 78, right: 56, top: LAYOUT.gridTop, bottom: 80 },
     tooltip: {
       trigger: 'axis',