mobile_facets/mobile_facets.module

<?php

use Drupal\Core\Render\AttachmentsTrait;

/**
 * Implements hook_page_attachments().
 */
function mobile_facets_page_attachments(array &$attachments) {
  $attachments['#attached']['library'][] = 'mobile_facets/mobile_facets';
}

/**
 * Implements hook_theme_registry_alter().
 */
function mobile_facets_theme_registry_alter(array &$theme_registry) {
  // Get the active theme name (optional: to target a specific theme).
  $active_theme = \Drupal::service('theme.manager')->getActiveTheme()->getName();
  
  // Optional: Restrict to a specific theme (e.g., 'my_custom_theme') to avoid affecting admin themes.
  // if ($active_theme !== 'my_custom_theme') {
  //   return;
  // }
  
  // Set the path for the 'region' theme hook to your module's templates directory.
  if (isset($theme_registry['region']['path'])) {
    $module_path = \Drupal::service('extension.list.module')->getPath('mobile_facets');
    $theme_registry['region']['path'] = $module_path . '/templates';
  }
}