- BackButton now accepts a `class` prop (default 'mb-4') so callers can
override spacing; resolves hardcoded margin in flex-row topbar snippets
- documents/[id]/edit and enrich/[id] pass class="" to suppress the margin
- Replace weak className unit test with class-prop behaviour tests
- Add [data-hydrated] comment in E2E spec explaining what emits the attribute
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>