Build the Workbench's package CSS apart from Tailwind

Plan step 37 review. @tailwindcss/vite inlines the imports of an entry
that uses Tailwind without Vite's skipDuplicates, so with all.css beside
@import 'tailwindcss' every shared component stylesheet repeated later in
the cascade (231 repeated rules; button.css's hover and disabled rules
thirteen times), and every browser test ran against an order no
application gets. workbench/resources/css/package.css now holds all.css
and the scheme in an entry Tailwind never touches, and app.css keeps
Tailwind for the showcase's classes. The built package CSS repeats no
rule, and the Workbench's CSS shrinks from 559 to 406 KB.

Both entries open with the same layer statement, properties first,
because Tailwind hoists that layer to the top of its output; the order
is the one the single entry had, whichever the page links first. The
showcase's Vite config, vite.config.js and the error page test's probe
manifest name the new entry.

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

tests/Feature/ErrorPagesTest.php

@@ -97,6 +97,7 @@ it('lets the application\'s own error view win', function () {
 it('loads the application\'s Vite entries', function () {
     File::ensureDirectoryExists($this->temporary.'/build');
     File::put($this->temporary.'/build/manifest.json', json_encode([
+        'workbench/resources/css/package.css' => ['file' => 'assets/package-probe.css', 'src' => 'workbench/resources/css/package.css', 'isEntry' => true],
         'workbench/resources/css/app.css' => ['file' => 'assets/app-probe.css', 'src' => 'workbench/resources/css/app.css', 'isEntry' => true],
         'workbench/resources/js/app.js' => ['file' => 'assets/app-probe.js', 'src' => 'workbench/resources/js/app.js', 'isEntry' => true],
     ]));
@@ -106,6 +107,7 @@ it('loads the application\'s Vite entries', function () {
 
     $this->get('/abort/404')
         ->assertNotFound()
+        ->assertSee('build/assets/package-probe.css', false)
         ->assertSee('build/assets/app-probe.css', false)
         ->assertSee('build/assets/app-probe.js', false)
         ->assertDontSee('data-md-error-fallback', false);