feat(onboarding): add A2 household setup page with responsive progress sidebar layout

Desktop: 300px ProgressSidebar (step 1 active) + flex form area.
Mobile: "Schritt 1 von 3" eyebrow + HouseholdSetupForm.
Also stubs /household/staples as redirect target for A3.

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

frontend/src/test-setup.ts

@@ -0,0 +1,7 @@
+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"] *' });