Add a clear button to the date picker

`clearable` empties a date, or both ends of a range, closes an open
picker and hands focus back to the field, as the time picker's does.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01V9NnLxnPp8vaaurb3Z1MFy

tests/Feature/Components/DatepickerTest.php

@@ -163,3 +163,12 @@ it('replaces the hint with the errors for the property and its start and end', f
         ->toContain('data-datepicker-error')
         ->and(substr_count($html, 'data-invalid=""'))->toBe(2);
 });
+
+it('offers a clear button on request', function () {
+    expect((string) $this->blade('<x-datepicker label="Expires" clearable />'))
+        ->toContain('data-field-clear')
+        ->toContain('x-on:click="clear()"')
+        ->toContain('aria-label="Clear"')
+        ->and((string) $this->blade('<x-datepicker label="Expires" />'))
+        ->not->toContain('data-field-clear');
+});