Plan step 25 (navigation Missing): M3's "hides on scroll-down, reappears on
scroll-up" had no implementation. `<x-navigation-bar hide-on-scroll>` slides the
bar out on the default spatial spring — an instant swap under reduced motion,
which zeroes the duration token — and never while a snackbar, a bottom sheet or
a drawer is anchored to its edge; focus reaching the bar brings it back.
`<x-app-shell hide-bar-on-scroll>` picks it, and --material-bottom-bar follows
the bar down and up so a `fab` button and the snackbar keep their offsets.
Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Qwx5USif3wFFmxtHg5U1g9
