Move the file picker's rules out of the field into file.css

<x-file> marks its field root data-md-file, and the tonal
::file-selector-button with its hover and disabled states moves from
field.css to components/file.css on the state tokens (plan step 36). A
browser test pins the field's 56px box and 16px padding and the pill.

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

resources/views/components/file.blade.php

@@ -4,7 +4,8 @@
      picker, a file dropped on it, the keyboard, what a screen reader announces, the `change` a
      Livewire upload listens for. So the input stays native, its label always floats (the button
      stands where a resting label would), and only its `::file-selector-button` is restyled: a tonal
-     pill, so it reads as the thing to press (resources/css/components/field.css).
+     pill, so it reads as the thing to press (resources/css/components/file.css, on the field's
+     chrome; the field's root carries `data-md-file`).
 
      The browser's own line beside the button ("No file chosen", "3 files") is drawn transparent:
      it cannot be truncated or wrapped, and the caller shows what was chosen anyway, as previews. A
@@ -28,7 +29,7 @@
         : [];
 @endphp
 
-<x-livewire-material::field :$id :$label :$hint :$messages :$variant floated :class="$attributes->get('class')">
+<x-livewire-material::field :$id :$label :$hint :$messages :$variant floated :class="$attributes->get('class')" data-md-file>
     <input
         {{ $attributes->except(['class', 'id', 'type']) }}
         type="file"