Give a segmented list item a fill that reads against the page

`ItemSegmentedContainerColor get() = ColorSchemeKeyTokens.Surface`
(ListTokens.kt, C-21) was taken literally, but foundation/base.css
paints the page `surface` too — so a segmented list was invisible on any
default page. The token reads against a Compose scaffold, not against
this package's own page.

The tile is `surface-container` now, the step M3 names for a container
that has to read against the page, and what 1.x drew. Found in
SealShare: the files chosen for an upload list under the drop zone with
nothing to set them apart from it.

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

tests/Feature/Components/ListTest.php

@@ -127,7 +127,7 @@ it('lays a row\'s state layer over its fill, so a selected or segmented row keep
         ->and($css->declarations('[data-md-list-row]:not([data-md-card]):has([data-md-list-open]:focus-visible)'))
         ->toHaveKey('background-color', 'color-mix(in srgb, currentColor calc(var(--md-sys-state-focus-state-layer-opacity) * 100%), var(--md-list-row-fill, transparent))')
         ->and($css->declarations(':where([data-md-list-row])'))->toBe(['--md-list-row-fill' => 'transparent'])
-        ->and($css->declarations("[data-md-list='segmented'] > [data-md-list-item]"))->toHaveKey('--md-list-row-fill', 'var(--md-sys-color-surface)')
+        ->and($css->declarations("[data-md-list='segmented'] > [data-md-list-item]"))->toHaveKey('--md-list-row-fill', 'var(--md-sys-color-surface-container)')
         ->and($css->declarations('[data-md-list-item][data-md-selected]'))->toHaveKey('--md-list-row-fill', 'var(--md-sys-color-secondary-container)')
         ->and(File::get(ComponentStylesheet::path('table')))->toContain('--md-list-row-fill: var(--md-sys-color-secondary-container);');