Lift the snackbar above a toolbar placed at the bottom

SealShare's only navigation is a floating toolbar at place="bottom". In
1.x it set --material-bottom-bar to lift the snackbar over it; in 2.0.0
the toolbar reads that variable to place itself, so an application can
no longer set it, and the snackbar landed on the toolbar. M3 nudges a
snackbar "upward to avoid overlapping FABs/docked toolbars" and never
puts one in front of navigation.

A bottom-placed toolbar now publishes --material-bottom-toolbar, the
distance from the window's bottom edge to its top: floating 64px (as
tall as an md or lg FAB beside it), docked 64px plus the safe area it
pads, rounded docked floating from 840px. It is declared on :root and
again on the scaffold's root, the only place its formula sees the bar.
The snackbar clears whichever of the bar and the toolbar reaches higher,
and a page pads its end with it. Two Chromium tests, both failing on the
old formula: a docked toolbar on a scaffold's navigation bar, and a
floating toolbar without a scaffold (plan step 46).

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

resources/views/components/toolbar.blade.php

@@ -25,7 +25,9 @@
      A docked toolbar and a navigation bar occupy the same region of the screen and M3 says never to
      show both at once: the bar belongs on a primary page, the toolbar on a secondary or contextual
      one. Either way a toolbar placed at `bottom` clears `--material-bottom-bar`, so it is never
-     buried under `<x-scaffold>`'s bar.
+     buried under `<x-scaffold>`'s bar. It publishes what it covers in turn, as
+     `--material-bottom-toolbar` (the distance from the window's bottom edge to its top): the
+     snackbar lifts above it, and a page pads its end with it.
 
      Put `<x-button icon="…" tooltip="…" />` controls in the slot (`:selected` for toggles). It is a
      `role="toolbar"`: the arrow keys move between its controls (resources/js/toolbar.js,