Shows undo notification after slot add/replace. Rückgängig button
calls onundo, auto-dismisses after 4s via ondismiss callback.
Also patches test-setup for userEvent + fake timers compatibility.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
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>