Rewrite humanize_delta as a symmetric past/future ladder with
sub-minute precision. Replace the bare ISO date fallback after 7 days
with a day-month form (year suppressed when same as now). Refs spec
docs/superpowers/specs/2026-05-16-timeago-shared-display-design.md.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
