Key the views on M3's window size classes, not Tailwind's

Plan step 15. Every `sm:`/`md:`/`lg:`/`xl:` in the components, the showcase
(sections, layout, shell) and the pagination and error views becomes the M3
window size class the audits' breakpoint maps prescribe: the full-screen
dialog, the FAB, the snackbar's width, `radio inline`, the section picker and
the page numbers move from 640px to `medium` (600px, M3's compact boundary,
N-07 / C-07 / IN-28); `button responsive` moves from 1024px to `expanded`
(840px); `section-nav`'s grid-to-row switch from 1280px to `large` (1200px,
N-07); and `drawer pane` from 1280px to `expanded`, where M3 shows two panes
for list-detail (C-07). The pane's default width is now 360dp, M3's fixed
supporting pane at expanded.

Showcase example grids take two columns from `medium` and three or more from
`expanded`; the showcase's own theme picker swaps at `expanded`, the nearest
class boundary to the 768px it used (no M3 rule applies to it).

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Qwx5USif3wFFmxtHg5U1g9

resources/views/showcase/sections/buttons.blade.php

@@ -77,7 +77,7 @@
             </x-button-group>
             BLADE,
         'A choice as a connected group' => <<<'BLADE'
-            <div x-data="{ theme: 'system', days: ['mon'] }" class="grid w-full gap-6 md:grid-cols-2">
+            <div x-data="{ theme: 'system', days: ['mon'] }" class="grid w-full gap-6 medium:grid-cols-2">
                 <x-group label="Theme" name="showcase-theme" x-model="theme" :options="[
                     ['id' => 'light', 'name' => 'Light', 'icon' => 'light_mode'],
                     ['id' => 'dark', 'name' => 'Dark', 'icon' => 'dark_mode'],