build(vite): stub ColorMaps.json.js with a default export

VolView's virtual-modules plugin stubs @kitware/vtk.js's internal
ColorMaps.json.js to drop the unused built-in colormap data. vtk.js v36
builds with Vite/Rolldown, which emits that module with `export default`
(v35's Rollup build used a minified named export). Match the new shape
so the stub satisfies ColorMaps.js's default import.

Author: PaulHax

vite.config.ts

@@ -131,7 +131,7 @@ export default defineConfig({
         if (id.includes('@kitware/vtk.js')) {
           if (id.includes('ColorMaps.json.js')) {
             // We don't use the built-in colormaps
-            return 'export const v = []';
+            return 'export default [];';
           }
 
           // We don't use these classes