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>

assets/js/core/pagination.js

@@ -14,7 +14,6 @@
 
     var triggerText = (window.aksrtData && aksrtData.ajaxTrigger) || "加载更多";
     var nomoreText = (window.aksrtData && aksrtData.ajaxNomore) || "没有更多了";
-    var loadingText = (window.aksrtData && aksrtData.ajaxLoading) || "正在加载...";
     var errorText = (window.aksrtData && aksrtData.ajaxLoadError) || "加载失败，请重试";
 
     containers.forEach(function (container) {
@@ -51,18 +50,37 @@
         target = container.parentElement.querySelector(".post-grid, .comment-list, .commentlist, .content-stream__list");
       }
 
+      // 参考主题兜底 loader：DOM 里没有骨架时补一个 .loading 转圈 + 文案，
+      // 绝不用按钮自身文字来表达加载态。
+      function fallbackLoader() {
+        var text = (window.aksrtData && aksrtData.ajaxLoading) || "加载中...";
+        return (
+          '<div class="mb20"><div class="text-center muted-2-color mt20">' +
+          '<i class="loading mr10"></i>' + text +
+          '</div></div>'
+        );
+      }
+
       function showSkeleton() {
         if (!target) return;
-        // PHP 产出下划线类名 post_ajax_loader；这里同时兼容连字符写法。
-        var loader = target.querySelector(".post_ajax_loader, .post-ajax-loader");
-        if (loader) {
-          loader.classList.add("is-loading");
+        var loader = target.querySelector(".post_ajax_loader");
+        if (!loader) {
+          loader = document.createElement("div");
+          loader.className = "post_ajax_loader";
+          loader.innerHTML = fallbackLoader();
         }
+        // 参考主题 beforeSend：骨架每次翻页都挪到列表末尾（分页控件之前），
+        // 紧贴最后一张卡片、位于「加载更多」按钮上方。
+        target.insertBefore(
+          loader,
+          container.parentNode === target ? container : null
+        );
+        loader.classList.add("is-loading");
       }
 
       function hideSkeleton() {
         if (!target) return;
-        var loader = target.querySelector(".post_ajax_loader, .post-ajax-loader");
+        var loader = target.querySelector(".post_ajax_loader");
         if (loader) {
           loader.classList.remove("is-loading");
         }
@@ -72,13 +90,11 @@
         container.classList.remove("ias-pending");
         if (markNomore && loadMoreBtn) {
           loadMoreBtn.innerHTML = nomoreText;
-          loadMoreBtn.classList.remove("is-loading");
           loadMoreBtn.classList.add("ajax-nomore");
           var nextWrap = loadMoreBtn.closest(".next-page");
           if (nextWrap) nextWrap.classList.add("no-more");
           loadMoreBtn.style.pointerEvents = "none";
         } else if (loadMoreBtn && !loadMoreBtn.classList.contains("ajax-nomore")) {
-          loadMoreBtn.classList.remove("is-loading");
           if (failed) {
             loadMoreBtn.textContent = errorText;
           } else {
@@ -93,7 +109,6 @@
         stopInfinite(false);
         if (loadMoreBtn) {
           loadMoreBtn.textContent = message || errorText;
-          loadMoreBtn.classList.remove("is-loading");
           loadMoreBtn.classList.remove("ajax-nomore");
           loadMoreBtn.style.pointerEvents = "";
         }
@@ -107,12 +122,8 @@
         }
 
         loading = true;
-        // 骨架开关统一走 .is-loading（modal-runtime.css），不要直接写
-        // display:flex —— 那会让卡片型骨架挤成一行而不是纵向堆叠。
-        if (loadMoreBtn) {
-          loadMoreBtn.classList.add("is-loading");
-          loadMoreBtn.textContent = loadingText;
-        }
+        // 加载态的呈现完全交给列表末尾的骨架（参考主题 post_ajax beforeSend
+        // 只操作 .post_ajax_loader，不触碰「加载更多」按钮自身的文字）。
         showSkeleton();
 
         var action = isComment ? "aksrt_load_more_comments" : "aksrt_load_more_posts";
@@ -199,7 +210,6 @@
             loading = false;
             hideSkeleton();
             if (loadMoreBtn && !loadMoreBtn.classList.contains("ajax-nomore") && !failed) {
-              loadMoreBtn.classList.remove("is-loading");
               loadMoreBtn.innerHTML = triggerText;
               if (mode === "infinite") {
                 var lazyTrigger = clickTarget.closest(".next-page") || clickTarget;