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/posts-renderer/markup.php

@@ -207,10 +207,27 @@ if (!function_exists('aksrt_render_mini_list')) {
 }
 
 if (!function_exists('aksrt_render_placeholder')) {
+	/**
+	 * 骨架屏占位（legacy zib_get_post_placeholder parity）。
+	 *
+	 * 骨架块复用真实卡片的 posts-item / post-graphic / item-body 结构与尺寸，
+	 * 只是把内容换成 .placeholder。列表模式四行（标题 k1、摘要 k2、两枚 s1），
+	 * 卡片模式三行（标题 t1、摘要 k2、两枚 s1），对应参考主题 1:1。
+	 *
+	 * @param string $mode  list|card|mini|mini_thumb。
+	 * @param int    $count 重复数量，1–12。
+	 */
 	function aksrt_render_placeholder(string $mode = 'list', int $count = 3): string {
 		$count = max(1, min(12, $count));
-		$class = $mode === 'card' ? 'posts-item card' : 'posts-item list flex';
-		$item = '<posts class="' . esc_attr($class) . '"><div class="post-graphic"><div class="item-thumbnail placeholder"></div></div><div class="item-body flex xx flex1 jsb"><div class="placeholder t1"></div><div class="placeholder k2"></div><div class="placeholder s1"></div></div></posts>';
+		if ($mode === 'mini') {
+			$item = '<div class="posts-mini"><div class="placeholder k1"></div></div>';
+		} elseif ($mode === 'mini_thumb') {
+			$item = '<div class="posts-mini"><div class="mr10"><div class="item-thumbnail placeholder"></div></div><div class="posts-mini-con flex xx flex1 jsb"><div class="placeholder t1"></div><div class="placeholder s1"></div></div></div>';
+		} elseif ($mode === 'card') {
+			$item = '<posts class="posts-item card ajax-item"><div class="post-graphic"><div class="radius8 item-thumbnail placeholder"></div></div><div class="item-body"><h2 class="item-heading item-excerpt placeholder t1"></h2><p class="mt10 placeholder k2"></p><i class="flex jsb"><i class="placeholder s1"></i><i class="placeholder s1 ml10"></i></i></div></posts>';
+		} else {
+			$item = '<posts class="posts-item list flex ajax-item"><div class="post-graphic"><div class="radius8 item-thumbnail placeholder"></div></div><div class="item-body flex xx flex1 jsb"><p class="placeholder t1"></p><h4 class="item-excerpt placeholder k1"></h4><p class="placeholder k2"></p><i><i class="placeholder s1"></i><i class="placeholder s1 ml10"></i></i></div></posts>';
+		}
 		return str_repeat($item, $count);
 	}
 }