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

@@ -8,12 +8,17 @@ use WPMultiCity\Redirect;
 /**
  * Isolated test for the DOING_AJAX bail-out in Redirect::handle().
  *
- * Must be in a separate file sorted AFTER RouterTest so that defining the
- * DOING_AJAX constant does not contaminate Router::route() tests in RouterTest,
- * which also bails early when DOING_AJAX is true.
+ * 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 ZRedirectDoingAjaxTest extends TestCase
+final class RedirectDoingAjaxTest extends TestCase
 {
+    /**
+     * @runInSeparateProcess
+     * @preserveGlobalState disabled
+     */
     public function test_bail_when_doing_ajax(): void
     {
         if (!\defined('DOING_AJAX')) {