Civi extension: register templates/ dir via hook_civicrm_config

The Engagement Report tab page renders templates/CRM/WebformMw/Page/Tab.tpl
via Smarty. Without an explicit template-dir registration, Smarty cannot
locate the file and the tab fails to render. Use CRM_Core_Smarty's
prependTemplateDir() (cleaner than splicing template_dir by hand).

Mirrors the same fix the CiviCRM admin applied on the server so the repo
source no longer drifts from the working deployed state.

civi-extension/webform-mw/webform_mw.php

@@ -37,6 +37,19 @@ function _webform_mw_staff_key(): string {
   return is_string($env) ? $env : '';
 }
 
+/**
+ * Implements hook_civicrm_config().
+ *
+ * Registers this extension's `templates/` directory with Smarty so the
+ * Engagement Report tab page can locate `CRM/WebformMw/Page/Tab.tpl`.
+ * Without this hook the page callback runs but Smarty has no idea where
+ * the template lives.
+ */
+function webform_mw_civicrm_config(&$config) {
+  $template = CRM_Core_Smarty::singleton();
+  $template->prependTemplateDir(__DIR__ . '/templates');
+}
+
 /**
  * Implements hook_civicrm_xmlMenu().
  *