* feat(breadcrumbs): collapse to parent back-link on mobile Mobile breadcrumbs wrapped across multiple lines on narrow screens. Now shows a single parent back-link with CaretLeft icon (44px touch target) on mobile, full trail on desktop. Removes redundant topic title from visual breadcrumbs on thread pages while preserving it in JSON-LD structured data via new jsonLdItems prop. * fix(breadcrumbs): update tests for dual mobile/desktop render Tests using getByText('Home') failed in CI because the mobile back-link and desktop breadcrumb list both render the same text. Switch to querying within the nav landmark or using getAllByRole.