The initial sheen (15% sheen / 9% base, 1.4s) was too subtle to read as
animation. Bump to a 5-stop gradient (22-24% sheen / 8% base, 1.25s), define
explicit light-mode --skeleton-base/--skeleton-sheen tokens (was relying on
fallbacks only), and give the tree glyph the same shimmering gradient so it
animates with the bars. prefers-reduced-motion still disables the sweep.