Move the textarea's rules out of the field into textarea.css

<x-textarea> marks its field root data-md-textarea, and what a
<textarea> changes in the field — the grip in the corner, the label on
the first line, autogrow between rows and max-rows, the filled offsets —
moves from field.css to components/textarea.css (plan step 36).

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Qwx5USif3wFFmxtHg5U1g9

resources/views/components/textarea.blade.php

@@ -5,7 +5,8 @@
      form's column never moves. The label rests on the first line rather than in the middle of the
      box. `label`, `hint`, `variant`, `counter` for M3's character counter against `maxlength`, and
      `full` to span the pane past the 40rem M3 bounds a field to from `medium`; every other
-     attribute reaches the `<textarea>`. --}}
+     attribute reaches the `<textarea>`. The field's root carries `data-md-textarea`; what a
+     textarea changes in the field's chrome is resources/css/components/textarea.css. --}}
 
 @props([
     'label' => null,
@@ -30,7 +31,7 @@
     $max = $counter ? $attributes->get('maxlength') : null;
 @endphp
 
-<x-livewire-material::field :$id :$label :$hint :hint-class="$hintClass" :$messages :$variant :counter="$max" :$full :class="$attributes->get('class')" :data-md-readonly="$attributes->get('readonly') ? '' : null">
+<x-livewire-material::field :$id :$label :$hint :hint-class="$hintClass" :$messages :$variant :counter="$max" :$full :class="$attributes->get('class')" :data-md-readonly="$attributes->get('readonly') ? '' : null" data-md-textarea>
     <textarea
         {{ $attributes->except(['class', 'id', 'placeholder']) }}
         id="{{ $id }}"