clarify textColor behaviour

Author: gzh2003

packages/grid/src/DataBarGridModel.ts

@@ -35,6 +35,11 @@ export interface DataBarOptions {
   columnMax: number;
   axis: AxisOption;
   color: GridColor | GridColor[];
+  /**
+   * The text color for the cell, resolved from format rules/bar color.
+   * If the user has explicitly set a text color via formatting, that color is used.
+   * Otherwise it defaults to the databar's bar color.
+   */
   textColor: GridColor;
   valuePlacement: ValuePlacementOption;
   opacity: number;