feat(wpmc 1.1.0): Redirect::handle reverse-slug lookup on is_404

Replace old triggering-on-page_new semantics with washanyanya-style:
- template_redirect@1 + is_404() trigger
- get_posts(name=$slug, post_type=page, status=[private,publish])
- match candidate.ID against page_unic[i].page_new
- 301 to /<town>/<orig-canonical-path>/

Closes Gitea issue #1.

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

tests/ZRedirectDoingAjaxTest.php

@@ -0,0 +1,30 @@
+<?php
+declare(strict_types=1);
+
+namespace WPMultiCity\Tests;
+
+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.
+ */
+final class ZRedirectDoingAjaxTest extends TestCase
+{
+    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);
+    }
+}