refactor(onboarding): remove aria-hidden workaround from progress sidebar

Replace getByText with getByRole(heading) in page test to disambiguate
the duplicate "Haushalt benennen" text between sidebar and form.
Revert defaultIgnore change in test-setup.ts.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/test-setup.ts

@@ -1,7 +1 @@
 import '@testing-library/jest-dom/vitest';
-import { configure } from '@testing-library/dom';
-
-// Exclude elements inside aria-hidden containers from text queries,
-// so that visually-hidden sidebars (e.g. ProgressSidebar in onboarding pages)
-// don't create duplicate text matches when the same text appears in the main content.
-configure({ defaultIgnore: 'script, style, [aria-hidden="true"] *' });