Variant orchestration
Parent label cascades; staggered children via `custom` + dynamic variants.
Toggle the parent below. Each <Item> inherits the parent's variant label via m.Provider, and its dynamic variant uses custom (the index) to compute a staggered delay.
- 0. fade
- 1. slide
- 2. scale
- 3. rotate
- 4. spring
- 5. tween