fix(wpmc 1.1.0): review polish — continue on bad permalink, ACF guard, drop suppress_filters, process-isolated AJAX test

- Redirect::handle: continue instead of return when get_permalink fails on a row (allow trying next row)
- Helpers::acf_ready() now public so Redirect can guard get_field('page_unic', ...) consistently
- Drop suppress_filters=false from get_posts (was risky on sites with query-altering plugins)
- @runInSeparateProcess for DOING_AJAX test (replaces Z-prefix ordering hack)

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

tests/RedirectDoingAjaxTest.php

@@ -0,0 +1,35 @@
+<?php
+declare(strict_types=1);
+
+namespace WPMultiCity\Tests;
+
+use WPMultiCity\Redirect;
+
+/**
+ * Isolated test for the DOING_AJAX bail-out in Redirect::handle().
+ *
+ * Isolation is achieved via @runInSeparateProcess on the test method, which
+ * forks a fresh PHP process so that defining the DOING_AJAX constant cannot
+ * contaminate other tests (e.g. RouterTest). The previous Z-prefix ordering
+ * hack is no longer needed.
+ */
+final class RedirectDoingAjaxTest extends TestCase
+{
+    /**
+     * @runInSeparateProcess
+     * @preserveGlobalState disabled
+     */
+    public function test_bail_when_doing_ajax(): void
+    {
+        if (!\defined('DOING_AJAX')) {
+            \define('DOING_AJAX', true);
+        }
+        \Brain\Monkey\Functions\stubs(['did_action' => 1]);
+        \Brain\Monkey\Functions\when('is_admin')->justReturn(false);
+        \Brain\Monkey\Functions\expect('wp_safe_redirect')->never();
+
+        Redirect::handle();
+
+        self::assertTrue(true);
+    }
+}