feat(wpmc S3): procedural wpmc_* API + smoke test

Also fixes PluginBootTest to be order-independent (reset booted flag)
and to expect ShortcodeDmr hook that boot() now wires.

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

tests/PluginBootTest.php

@@ -14,7 +14,13 @@ final class PluginBootTest extends TestCase
             eval('class ACF {}');
         }
 
-        Plugin::instance()->boot();
+        // Reset booted flag so this test is order-independent.
+        $plugin = Plugin::instance();
+        $reflection = new \ReflectionClass($plugin);
+        $prop = $reflection->getProperty('booted');
+        $prop->setValue($plugin, false);
+
+        $plugin->boot();
 
         self::assertNotFalse(
             has_action('init', ['WPMultiCity\\Taxonomy', 'do_register']),
@@ -28,6 +34,10 @@ final class PluginBootTest extends TestCase
             has_action('acf/init', ['WPMultiCity\\FieldGroup', 'do_register']),
             'boot() must register FieldGroup on acf/init'
         );
+        self::assertNotFalse(
+            has_action('init', ['WPMultiCity\\ShortcodeDmr', 'do_register']),
+            'boot() must register ShortcodeDmr on init'
+        );
     }
 
     public function test_boot_is_idempotent_when_called_multiple_times(): void
@@ -55,6 +65,9 @@ final class PluginBootTest extends TestCase
         \Brain\Monkey\Actions\expectAdded('acf/init')
             ->with([\WPMultiCity\FieldGroup::class, 'do_register'])
             ->once();
+        \Brain\Monkey\Actions\expectAdded('init')
+            ->with([\WPMultiCity\ShortcodeDmr::class, 'do_register'])
+            ->once();
 
         $plugin->boot();
         $plugin->boot();