Avatar with initials vs question-mark fallback, for-you marker
visibility, data-variant matrix (simple/for-you/rollup/comment),
count badge for rollup, comment preview rendering with fallback,
document title link, default vs comment-deep-link href, time-range
label for rollup with happenedAtUntil.
11 tests covering ~40 of ChronikRow's high-uncovered branches.
Refs #496.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
