fix(posts): repair the load-more skeleton and align it with the reference

Clicking 加载更多 showed no skeleton at all, and the placeholder shape did
not match the reference theme's post cards.

- Class-name mismatch: pagination.js queried .post-ajax-loader while every
  PHP producer emits .post_ajax_loader, so showSkeleton() never found a
  target and the loader stayed hidden. Accept both spellings.
- Inline display:none on the loader (pagination, comments, widget tab
  panes) outranked .is-loading, so even the correct selector could not
  reveal it. Drop the inline style; the reference uses a bare
  <div class="post_ajax_loader"> and toggles visibility from JS.
- loadNextPage() set indicator.style.display = "flex", which forced the
  .posts-item.card skeleton blocks (inline-block layout) into a single
  row instead of stacking vertically — the visible symptom. Remove those
  inline writes and drive .is-loading from CSS for every surface.
- Scope the hide/show rules on the class itself rather than requiring an
  .ajaxpager ancestor: homepage tab panes, archive streams and comment
  lists sit at three different depths.
- Rebuild aksrt_render_placeholder() on zib_get_post_placeholder's
  structure — list = t1/k1/k2 + two s1, card = t1 item-heading/k2 + two
  s1, thumb wrapped in post-graphic + radius8 item-thumbnail, all carrying
  ajax-item so the loader is not mistaken for a real card.
- Add mini/mini_thumb modes so ContentRenderer::placeholder() stops
  hand-rolling the same markup; normalize its 'lists' arg to 'list'.

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

inc/helpers/aksrt-comments.php

@@ -640,7 +640,8 @@ if (!function_exists('aksrt_get_comment_ajax_loader')) :
 	 */
 	function aksrt_get_comment_ajax_loader(): string {
 		$item = '<ul class="list-inline flex"><div class="avatar-img placeholder radius"></div><li class="flex1"><div class="placeholder s1 mb6" style="width: 30%;"></div><div class="placeholder k2 mb10"></div><i class="placeholder s1 mb6"></i><i class="placeholder s1 mb6 ml10"></i></li></ul>';
-		return '<div style="display:none;" class="post_ajax_loader">' . $item . $item . $item . $item . '</div>';
+		// 显隐交给 modal-runtime.css 的 .is-loading，内联 display:none 会让骨架永远无法展开。
+		return '<div class="post_ajax_loader">' . $item . $item . $item . $item . '</div>';
 	}
 endif;