feat: implement global autoresponder plugin

tests/package_contents_test.php

@@ -0,0 +1,9 @@
+<?php
+declare(strict_types=1);
+
+test('packing guidelines exclude docs and require manual icon', function (): void {
+    $packing = file_get_contents(dirname(__DIR__, 2) . '/PACKING.md') ?: '';
+    assert_contains('docs/dokumentacja.html', $packing);
+    assert_contains('must not contain `docs/`', $packing);
+    assert_contains('src/images/user_icon.svg', $packing);
+});