Size the loading indicator and publish the rail's value

Two gaps found rewriting the Boost skill for 2.0's plain CSS, each
closed the way M3 describes it.

`<x-loading size="96">`: M3 gives the loading indicator a responsive
size, 48dp by default and flexible from 24 to 240dp ("never exceed that
range"), with the container and the active shape in a fixed ratio. The
size had no prop, so an application wrote a width and height of its own;
`size` now takes a whole number of px in that range, written as
`--md-loading-size`, and the SVG keeps the 48:38 ratio as it scales. A
value outside the range is ignored, as `<x-icon>` and `<x-shape>` ignore
theirs, and an application's own width and height still win.

`--md-navigation-rail-value`: M3 Expressive's rail has two values,
collapsed and expanded (Compose's WideNavigationRailValue), and content
in a rail follows it. Without a hook an application copied the rail's
seven conditions — mode, `data-rail`, `data-rail-auto`, open, and the
window band — out of navigation-rail.css. The rail now publishes the
answer from the same branches that narrow it: `expanded` by default,
`collapsed` wherever it is drawn collapsed, so a style query in the
application's CSS switches at the first paint and at the same moment
as the rail's own items. A rail open over a scrim reads `expanded`, and
outside a rail the property is unset. A JS attribute would have missed
the first paint; a width container query would have lagged the collapse
animation.

Style queries on a custom property need Firefox 151, so the browser
floor moves from Firefox 147 to 151 (README, the CI note, UPGRADE's new
2.1.0 section); Chrome 125 and Safari 18.4 are unchanged.

Browser tests pin both in Chrome, Firefox and Safari: the indicator's
drawn box at 96 and 32px, and the rail's value — with a style query
acting on it — at the first paint for fixed modes, across the window
classes and the menu button for an adaptive rail, and open and closed
for a modal one. NavigationRailTest pins the value in each of the five
collapsed branches.

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

resources/views/components/loading.blade.php

@@ -1,8 +1,12 @@
 {{-- M3 Expressive's loading indicator: a shape that morphs through seven Expressive shapes while
      it turns, for a wait that has no known length.
 
-     In the text colour — primary unless the caller colours it — and 48px unless the caller's CSS
-     sizes it. `contained` puts it on a primary-container circle, for a spinner over content. It
+     In the text colour — primary unless the caller colours it — and 48px, M3's default. `size` is
+     its size in px, any whole number from 24 to 240, M3's responsive range ("never exceed that
+     range"; scale it up for large and extra-large windows): the container and the shape keep
+     their 48:38 ratio at every size, because the drawing scales with its box. It is written as
+     `--md-loading-size`; anything outside the range is ignored, and without it the caller's CSS
+     may size it. `contained` puts it on a primary-container circle, for a spinner over content. It
      is a `progressbar` named `label` ("Loading" by default); pass `:label="false"` where something
      else already says what is happening, as a button's own spinner does.
 
@@ -16,15 +20,18 @@
 @props([
     'contained' => false,
     'label' => null,
+    'size' => null,
 ])
 
 @php
+    $size = filter_var($size, FILTER_VALIDATE_INT, ['options' => ['min_range' => 24, 'max_range' => 240]]) ?: null;
     $decorative = $label === false;
     $label = $decorative ? null : ($label ?? __('Loading'));
 
     $attributes = $attributes->merge(array_filter([
         'data-md-loading' => true,
         'data-md-contained' => $contained ? true : null,
+        'style' => $size !== null ? "--md-loading-size: {$size}px" : null,
         'role' => $decorative ? null : 'progressbar',
         'aria-label' => $label,
         'aria-hidden' => $decorative ? 'true' : null,