build(web): upgrade Vitest 3→4 (browser-playwright provider) (#46)

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

web/vite.config.ts

@@ -5,6 +5,7 @@ import path from "node:path";
 import { defineConfig } from "vite";
 import { fileURLToPath } from 'node:url';
 import { storybookTest } from '@storybook/addon-vitest/vitest-plugin';
+import { playwright } from '@vitest/browser-playwright';
 const dirname = typeof __dirname !== 'undefined' ? __dirname : path.dirname(fileURLToPath(import.meta.url));
 
 // More info at: https://storybook.js.org/docs/next/writing-tests/integrations/vitest-addon
@@ -48,7 +49,7 @@ export default defineConfig({
         browser: {
           enabled: true,
           headless: true,
-          provider: 'playwright',
+          provider: playwright(),
           instances: [{
             browser: 'chromium'
           }]