Subscribe CTA

Control pops in over 0.35s → cursor arcs in over 0.8s to interact → state flips + confirmation motion (YouTube turns gray "Subscribed" + bell swings ±16° with decay / Bilibili long-press 0.55s progress ring fills then three icons light up at 0.2s intervals / generic capsule turns "Following" + checkmark draws in over 0.36s); each single style completes within 3s then auto-fades out