Plan step 32. Since containment.md C-12 the carousel defaults to M3's 16dp
of content padding, and Compose's createShiftedKeylineListForContentPadding
shrinks every keyline near the ends by a share of it, so a large item at
rest at the start or the end is masked by 1.33px a side in the showcase.
The tests asked for a zero inset there and failed; `open(i)` asks whether
an item is at the largest size any item has at that position. The helper's
list of showcase carousels gains the multi-aspect one.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Qwx5USif3wFFmxtHg5U1g9
