feat: Add comprehensive dark mode support for chart thumbnails and examples (#35111)

Co-authored-by: Claude <noreply@anthropic.com>

superset-frontend/plugins/plugin-chart-echarts/src/Sunburst/index.ts

@@ -19,10 +19,13 @@
 import { Behavior, t } from '@superset-ui/core';
 import transformProps from './transformProps';
 import thumbnail from './images/thumbnail.png';
+import thumbnailDark from './images/thumbnail-dark.png';
 import controlPanel from './controlPanel';
 import buildQuery from './buildQuery';
 import example1 from './images/Sunburst1.png';
+import example1Dark from './images/Sunburst1-dark.png';
 import example2 from './images/Sunburst2.png';
+import example2Dark from './images/Sunburst2-dark.png';
 import { EchartsChartPlugin } from '../types';
 
 export default class EchartsSunburstChartPlugin extends EchartsChartPlugin {
@@ -42,7 +45,10 @@ export default class EchartsSunburstChartPlugin extends EchartsChartPlugin {
         description: t(
           'Uses circles to visualize the flow of data through different stages of a system. Hover over individual paths in the visualization to understand the stages a value took. Useful for multi-stage, multi-group visualizing funnels and pipelines.',
         ),
-        exampleGallery: [{ url: example1 }, { url: example2 }],
+        exampleGallery: [
+          { url: example1, urlDark: example1Dark },
+          { url: example2, urlDark: example2Dark },
+        ],
         name: t('Sunburst Chart'),
         tags: [
           t('ECharts'),
@@ -51,6 +57,7 @@ export default class EchartsSunburstChartPlugin extends EchartsChartPlugin {
           t('Featured'),
         ],
         thumbnail,
+        thumbnailDark,
       },
       transformProps,
     });