Rewrite the divider without Tailwind

Plan step 36 (containment group): <x-divider> moves its class lists
into resources/css/components/divider.css, keyed on data-md-divider,
data-md-orientation, data-md-inset/middle and data-md-divider-heading/
-text for the subheader form (DividerTokens.kt; docs/reference/m3
§ Divider). Imported from the Containment block of components.css.

Hooks renamed: none of divider's own (it had no data-* hooks before),
but its rendered attribute order moved data-md-* ahead of role/aria-*,
which ToolbarTest.php's regex for a toolbar's vertical divider depended
on; fixed in the same commit. form.css picks up the @import './divider.css'
its TODO(step 36) marker was waiting on, since form.blade.php renders
<x-divider> and divider.css now carries the material.components layer.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Qwx5USif3wFFmxtHg5U1g9

tests/Feature/Components/ToolbarTest.php

@@ -14,7 +14,7 @@ it('gives a docked toolbar the rounded large-screen form on request, and only a
     expect($docked)
         ->toMatch('/role="toolbar"[^>]*data-variant="docked"\s+data-rounded/')
         // The divider between two groups is the toolbar's child, where toolbar.css stands it up.
-        ->toMatch('/role="toolbar".*aria-label="Undo".*<div\s+role="separator" aria-orientation="vertical"[^>]*>\s*<\/div>.*aria-label="Bold"/s')
+        ->toMatch('/role="toolbar".*aria-label="Undo".*<div\s+data-md-divider\s+data-md-orientation="vertical"\s+role="separator" aria-orientation="vertical"[^>]*>\s*<\/div>.*aria-label="Bold"/s')
         ->and((string) $this->blade('<x-toolbar rounded><x-button icon="undo" tooltip="Undo" /></x-toolbar>'))
         ->toContain('data-variant="floating"')
         ->not->toContain('data-rounded')