feat(chart): support per-track legend positions

src/components/core/layout.ts

@@ -371,6 +371,7 @@ export function buildTrackLayouts(options: BuildTrackLayoutsOptions): TrackLayou
     })
 
     return {
+      id: displayTrack.id,
       index,
       series,
       seriesList: displayTrack.visibleSeries,

src/components/core/types.ts

@@ -72,6 +72,8 @@ export interface HoveredSeriesPoint extends DisplaySeries {
  * 轨道布局
  */
 export interface TrackLayout {
+  /** Stable track key derived from trackId, or from the series id when trackId is omitted. */
+  id: string
   index: number
   series: DisplaySeries
   /** Visible series used by rendering and interaction code. */