feat(wpmc S2): register taxonomy town with required args

Also stub translation functions in base TestCase so __() calls from
WPMultiCity namespace resolve correctly via Brain Monkey.

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

includes/class-taxonomy.php

@@ -14,6 +14,24 @@ final class Taxonomy
 
     public static function do_register(): void
     {
-        // Implementation filled in Task 5.
+        register_taxonomy(self::SLUG, ['shortcode-town'], [
+            'labels'             => [
+                'name'          => __('Города', 'wp-multi-city'),
+                'singular_name' => __('Город', 'wp-multi-city'),
+                'menu_name'     => __('Города', 'wp-multi-city'),
+                'add_new_item'  => __('Добавить', 'wp-multi-city'),
+            ],
+            'public'             => false,
+            'publicly_queryable' => false,
+            'hierarchical'       => false,
+            'show_ui'            => true,
+            'show_in_menu'       => true,
+            'show_in_nav_menus'  => false,
+            'show_admin_column'  => false,
+            'show_in_rest'       => true,
+            'query_var'          => false,
+            'rewrite'            => false,
+            'meta_box_cb'        => false,
+        ]);
     }
 }