fix(pagination): align AJAX load-more loading state with reference

Loading indication now matches the reference theme's post_ajax() contract:

- Stop overwriting the 加载更多 button label with 正在加载...; the button
  keeps its own text and the .post_ajax_loader skeleton carries the busy
  state instead.
- Add the reference fallback loader (.loading ring + 加载中...) when no
  skeleton exists in the DOM, and reinsert the skeleton after the last
  card on every page load like beforeSend does.
- Retext the loader string to 加载中... (zib__('loading')) and make the
  ajax_trigger default a translatable string.
- Route ajax-list.js / comments.js / widgets frontend.js through the
  .is-loading class instead of inline display, which outranked the class
  rule and could freeze the skeleton shut.
- Drop the search.php inline display:none that defeated .is-loading, and
  remove the unproduced .post-ajax-loader / [data-aksrt-ajax-loader] shims.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/Core/ScriptsPart1c.php

@@ -463,10 +463,11 @@ trait ScriptsPart1c {
             'debugLog'              => defined('WP_DEBUG') && WP_DEBUG && defined('WP_DEBUG_LOG') && WP_DEBUG_LOG,
             'postPaginationMode'    => class_exists('\AKSRT\Settings\Settings') ? \AKSRT\Settings\Settings::get_post_pagination_mode() : 'load_more',
             'commentPaginationMode' => class_exists('\AKSRT\Settings\Settings') ? \AKSRT\Settings\Settings::get_comment_pagination_mode() : 'numbered',
-            // AJAX 翻页文案
-            'ajaxTrigger'           => (class_exists('\AKSRT\Settings\Settings') && ($t = \AKSRT\Settings\Settings::get_post_list_style_settings()['ajax_trigger'] ?? '') !== '') ? $t : '<i class="fa fas fa-angle-right"></i>加载更多',
+            // AJAX 翻页文案（参考主题 zib__('load_more') / 'ajax_nomore'）
+            'ajaxTrigger'           => (class_exists('\AKSRT\Settings\Settings') && ($t = \AKSRT\Settings\Settings::get_post_list_style_settings()['ajax_trigger'] ?? '') !== '') ? $t : '<i class="fa fas fa-angle-right"></i>' . __('加载更多', 'aksrt'),
             'ajaxNomore'            => (class_exists('\AKSRT\Settings\Settings') && ($n = \AKSRT\Settings\Settings::get_post_list_style_settings()['ajax_nomore'] ?? '') !== '') ? $n : __('没有更多内容了', 'aksrt'),
-            'ajaxLoading'           => __('正在加载...', 'aksrt'),
+            // 骨架兜底文案，仅在没有 post_ajax_loader 时使用（参考主题 zib__('loading')）。
+            'ajaxLoading'           => __('加载中...', 'aksrt'),
             'iasMax'                => class_exists('\AKSRT\Settings\Settings') ? \AKSRT\Settings\Settings::get_post_list_style_settings()['ias_max'] : 3,
             'commentIasAuto'        => class_exists('\AKSRT\Settings\Settings') ? \AKSRT\Settings\Settings::get_comment_display_settings()['paging_ajax_ias'] : true,
             'commentUploadUrl'       => esc_url_raw(rest_url('aksrt/v1/comment/upload-image')),