feat: add cylinder carousel with concave and convex variants

[starc007]

What

New `cylinder-carousel` component (motion category): a draggable carousel whose round items ride the wall of a cylinder.

• Concave (default): inside of the cylinder — center ball smallest, dipped into a valley, balls grow and climb toward the edges. Horizontal motion follows an interior perspective projection (slow through the center, accelerating off the edges).
• Convex: outside of the cylinder — center ball biggest on an arch, shrinking evenly to the edges with uniform spacing.

Details

• Drag (1:1), wheel, and arrow keys; release hands pointer velocity to a soft spring with momentum projection and snap to the nearest item.
• Infinite wrap; exactly `visibleItems` in frame plus a half-visible ball straddling each edge.
• Auto-fit: `itemSize` is a cap — balls shrink so the row keeps breathing room at any container width (ResizeObserver).
• Off-stage balls set `visibility: hidden` so canvas/shader children stop painting; stage clips via `clip-path` (reliably clips GPU-composited children).
• Reduced motion: no glide, direct snap.
• Preview: 8 ShaderBackground circles with a Concave/Convex segment toggle.

Checks

• `bun run check` clean (typecheck, lint, registry — 41 components).