feat(wpmc S5): TitleFilter hooks the_title + single_cat_title do_shortcode

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

includes/class-title-filter.php

@@ -0,0 +1,13 @@
+<?php
+declare(strict_types=1);
+
+namespace WPMultiCity;
+
+final class TitleFilter
+{
+    public static function register(): void
+    {
+        \add_filter('the_title', 'do_shortcode', 9999);
+        \add_filter('single_cat_title', 'do_shortcode', 9999);
+    }
+}

tests/TitleFilterTest.php

@@ -0,0 +1,31 @@
+<?php
+declare(strict_types=1);
+
+namespace WPMultiCity\Tests;
+
+use WPMultiCity\TitleFilter;
+
+final class TitleFilterTest extends TestCase
+{
+    public function test_register_attaches_the_title_do_shortcode_at_9999(): void
+    {
+        TitleFilter::register();
+
+        self::assertSame(
+            9999,
+            has_filter('the_title', 'do_shortcode'),
+            'TitleFilter::register() must hook the_title → do_shortcode at priority 9999'
+        );
+    }
+
+    public function test_register_attaches_single_cat_title_do_shortcode_at_9999(): void
+    {
+        TitleFilter::register();
+
+        self::assertSame(
+            9999,
+            has_filter('single_cat_title', 'do_shortcode'),
+            'TitleFilter::register() must hook single_cat_title → do_shortcode at priority 9999'
+        );
+    }
+}