Extends the seeding pattern from the a11y spec: beforeAll creates two
persons + one document so the page renders the row layout. The
structural test now asserts the ConversationThumbnail tile AND the
DistributionBar are present — a regression that drops to the hero
or breaks the row wiring fails here instead of silently passing a
hero-state check.
Snapshot block stays gated on VISUAL=1 (baselines captured during
review against a seeded backend) so the structural coverage ships
immediately and the pixel-diff coverage ships once baselines land.
Refs #305
Fixes @saraholt blocker 2 from PR review
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>