fix(chart): refine ECharts series styling and legend color handling across bar, donut, and radar charts

ts_web/elements/00group-chart/dees-chart-echarts-base.ts

@@ -87,12 +87,17 @@ export abstract class DeesChartEchartsBase extends DeesElement {
     if (!this.chartInstance) return;
     const themeOptions = getEchartsThemeOptions(this.goBright);
     const chartOption = this.buildOption();
-    // Merge theme defaults with chart-specific options
+    // Deep-merge theme defaults with chart-specific options for nested objects
     const merged = {
       ...themeOptions,
       ...chartOption,
       textStyle: { ...themeOptions.textStyle, ...(chartOption.textStyle || {}) },
       tooltip: { ...themeOptions.tooltip, ...(chartOption.tooltip || {}) },
+      legend: {
+        ...themeOptions.legend,
+        ...(chartOption.legend || {}),
+        textStyle: { ...(themeOptions.legend?.textStyle || {}), ...(chartOption.legend?.textStyle || {}) },
+      },
     };
     this.chartInstance.setOption(merged, true);
   }