feat(wpmc S4): OptionsPage scaffold + main_town_slug filter wiring

tests/OptionsPageTest.php

@@ -0,0 +1,29 @@
+<?php
+declare(strict_types=1);
+
+namespace WPMultiCity\Tests;
+
+use WPMultiCity\OptionsPage;
+
+final class OptionsPageTest extends TestCase
+{
+    public function test_register_attaches_acf_init_action(): void
+    {
+        OptionsPage::register();
+
+        self::assertNotFalse(
+            has_action('acf/init', [OptionsPage::class, 'do_register']),
+            'OptionsPage::register() must hook acf/init'
+        );
+    }
+
+    public function test_register_attaches_main_town_slug_filter(): void
+    {
+        OptionsPage::register();
+
+        self::assertNotFalse(
+            has_filter('wpmc_main_town_slug', ['WPMultiCity\\Helpers', 'main_town_slug']),
+            'OptionsPage::register() must hook wpmc_main_town_slug filter'
+        );
+    }
+}