Stub scrollTo in Vitest setup

- Silence jsdom's not-implemented warning during router-driven tests
- Keep the fix in test bootstrap only so runtime behavior stays unchanged

webui/vitest.setup.ts

@@ -1 +1,7 @@
 import '@testing-library/jest-dom/vitest';
+import { vi } from 'vitest';
+
+Object.defineProperty(window, 'scrollTo', {
+  value: vi.fn(),
+  writable: true,
+});