Move relativeTime from notifications.ts (Intl.RelativeTimeFormat) to a
new time.ts that uses the Paraglide comment_time_* message keys — the
same logic that was already in CommentThread's timeAgo(). Remove the
duplicate timeAgo() from CommentThread and re-export relativeTime from
notifications.ts for backwards compatibility.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>