Message Growth visualization: reset flicker, horizontal scrollbar, and inconsistent chip animation

[cloud-of-equality]

before.mov

Three issues in the "Message Growth" home-page visualization (web/src/components/architecture/message-flow.tsx):

1. Flicker at len=0/1. On restart the array snaps back to empty right after it starts regrowing, so it stutters instead of growing cleanly.
2. Scrollbar at len=8. The 8 chips overflow the container, adding a horizontal scrollbar and clipping assistant (final).
3. Inconsistent entrance (minor). Each chip's background slides in (width) while its label zooms in (scale) — two mismatched motions.