feat(wpmc S4): TermMeta registers ACF main_page_alt on taxonomy town

Add acf-stubs.php + TestCase::setUp() require-after-Patchwork pattern so
acf_add_local_field_group is Patchwork-instrumented and re-interceptable
across FieldGroupTest and TermMetaTest in the same PHP process.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

includes/class-term-meta.php

@@ -0,0 +1,44 @@
+<?php
+declare(strict_types=1);
+
+namespace WPMultiCity;
+
+final class TermMeta
+{
+    public const GROUP_KEY = 'group_wpmc_town_main_page';
+
+    public static function register(): void
+    {
+        add_action('acf/init', [self::class, 'do_register']);
+    }
+
+    public static function do_register(): void
+    {
+        if (!function_exists('acf_add_local_field_group')) {
+            return;
+        }
+        acf_add_local_field_group([
+            'key'    => self::GROUP_KEY,
+            'title'  => 'WPMultiCity / Town main page',
+            'fields' => [
+                [
+                    'key'           => 'field_wpmc_main_page_alt',
+                    'label'         => __('Главная страница для этого города', 'wp-multi-city'),
+                    'name'          => 'main_page_alt',
+                    'type'          => 'post_object',
+                    'post_type'     => ['page'],
+                    'return_format' => 'id',
+                    'allow_null'    => 1,
+                    'multiple'      => 0,
+                ],
+            ],
+            'location'   => [
+                [['param' => 'taxonomy', 'operator' => '==', 'value' => 'town']],
+            ],
+            'menu_order' => 0,
+            'position'   => 'normal',
+            'style'      => 'default',
+            'active'     => true,
+        ]);
+    }
+}