Add an illustration slot to the empty state

An application with its own artwork for an empty collection puts it in
the `illustration` slot, which is drawn in place of the shape and icon.
The slot's attributes go on the element around it, so its class sets the
colour an SVG's currentColor takes. A slot holding only whitespace or
comments counts as empty (hasActualContent), and without the slot the
empty state renders as before.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01RHoXZSHc8gGpZjFmA5fPc2

tests/Feature/Components/EmptyStateTest.php

@@ -15,3 +15,34 @@ it('sets an icon on an Expressive shape above its words and action', function ()
         ->toContain('Upload files')
         ->and(substr_count($html, '<svg'))->toBe(2);
 });
+
+it('draws an illustration in place of the shape and icon', function () {
+    $html = (string) $this->blade(<<<'BLADE'
+        <x-empty-state icon="upload_file" title="No routes yet">
+            <x-slot:illustration class="text-primary"><svg class="size-32" viewBox="0 0 10 10" aria-hidden="true"><circle cx="5" cy="5" r="4" /></svg></x-slot:illustration>
+        </x-empty-state>
+        BLADE);
+
+    expect($html)
+        ->toContain('<div class="text-primary"><svg class="size-32" viewBox="0 0 10 10" aria-hidden="true"><circle cx="5" cy="5" r="4" /></svg></div>')
+        ->not->toContain('text-secondary-container')
+        ->not->toContain('text-on-secondary-container')
+        ->toContain('No routes yet')
+        ->and(substr_count($html, '<svg'))->toBe(1);
+});
+
+it('keeps the shape and icon while the illustration slot holds nothing but comments', function () {
+    $html = (string) $this->blade(<<<'BLADE'
+        <x-empty-state title="No shares yet">
+            <x-slot:illustration>
+                <!-- artwork to come -->
+            </x-slot:illustration>
+        </x-empty-state>
+        BLADE);
+
+    expect($html)
+        ->toContain('text-secondary-container')
+        ->toContain('text-on-secondary-container')
+        ->not->toContain('artwork to come')
+        ->and(substr_count($html, '<svg'))->toBe(2);
+});