feat(wpmc S4): Router scaffold + query_vars filter for town

includes/class-router.php

@@ -0,0 +1,24 @@
+<?php
+declare(strict_types=1);
+
+namespace WPMultiCity;
+
+final class Router
+{
+    public static function register(): void
+    {
+        \add_action('wp', [self::class, 'route'], 9999);
+        \add_filter('query_vars', [self::class, 'add_town_query_var']);
+    }
+
+    public static function add_town_query_var(array $vars): array
+    {
+        $vars[] = 'town';
+        return $vars;
+    }
+
+    public static function route(): void
+    {
+        // Implementation in Tasks 10-13.
+    }
+}

tests/RouterTest.php

@@ -0,0 +1,38 @@
+<?php
+declare(strict_types=1);
+
+namespace WPMultiCity\Tests;
+
+use WPMultiCity\Router;
+
+final class RouterTest extends TestCase
+{
+    public function test_register_attaches_wp_action_at_priority_9999(): void
+    {
+        Router::register();
+
+        self::assertSame(
+            9999,
+            has_action('wp', [Router::class, 'route']),
+            'Router::register() must hook wp action at priority 9999'
+        );
+    }
+
+    public function test_register_attaches_query_vars_filter(): void
+    {
+        Router::register();
+
+        self::assertNotFalse(
+            has_filter('query_vars', [Router::class, 'add_town_query_var']),
+            'Router::register() must hook query_vars filter'
+        );
+    }
+
+    public function test_add_town_query_var_appends_town(): void
+    {
+        $vars = ['p', 'page_id'];
+        $result = Router::add_town_query_var($vars);
+
+        self::assertContains('town', $result);
+    }
+}