Smooth the page's text in the foundation, not per surface

The showcase and the error pages set grayscale font smoothing on
themselves, but the foundation did not, so an application that dropped
Tailwind's antialiased class rendered heavier text on macOS than the
package's own pages, silently. base.css now sets it on the page; the
showcase's and error page's copies go, and the guard tells a leftover
antialiased class to go too. Decided with the user (plan step 46).

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

tests/Feature/StylesheetsTest.php

@@ -212,6 +212,16 @@ it('brings every foundation file and text.css into the foundation, and nothing e
         ->and(array_values(preg_grep('/^components\//', $foundation)))->toBe([]);
 });
 
+it('paints the page in surface and on-surface, in the brand typeface, smoothed in grayscale', function () {
+    // An application drops Tailwind's `antialiased` with nothing to replace it: the showcase and the
+    // error pages, which set it themselves before, read it from here too.
+    $base = (string) preg_replace('~/\*.*?\*/~s', '', (string) file_get_contents(stylesheetPath('foundation/base.css')));
+
+    expect($base)->toMatch('/html \{\s*background-color: var\(--md-sys-color-surface\);\s*color: var\(--md-sys-color-on-surface\);\s*font-family: var\(--md-ref-typeface-brand\);\s*-webkit-font-smoothing: antialiased;\s*-moz-osx-font-smoothing: grayscale;\s*\}/')
+        ->and((string) file_get_contents(stylesheetPath('showcase.css')).file_get_contents(stylesheetPath('components/error-page.css')))
+        ->not->toContain('font-smoothing');
+});
+
 it('leaves no stylesheet under resources/css/ outside all.css or showcase.css', function () {
     // The full tree now that Tailwind is gone (plan step 39): every .css file on disk, not just the
     // ones a bundler happens to reach — a stray or orphaned file would show up here even though