feat(frontend): illustrated null states and author rewards fallback

Add aksrt_get_null / widget null helpers with null.svg, use them in
sidebar widgets, comments empty, and related posts; when PM is off show
post rewards entry on the single author bar.

inc/helpers/aksrt-single-render.php

@@ -555,6 +555,17 @@ if (!function_exists('aksrt_single_render_related')) :
 		$query = new WP_Query($args);
 		if (!$query->have_posts()) {
 			wp_reset_postdata();
+			$empty_wrap = 'theme-box relates' . ($style === 'img' ? ' relates-thumb' : '');
+			?>
+			<div class="<?php echo esc_attr($empty_wrap); ?>">
+				<div class="box-body notop">
+					<div class="title-theme"><?php echo esc_html($title); ?></div>
+				</div>
+				<div class="zib-widget">
+					<?php echo function_exists('aksrt_get_null') ? aksrt_get_null(__('暂无相关文章', 'aksrt'), 40, 'null.svg', 'related-null', 220) : ''; // phpcs:ignore WordPress.Security.EscapeOutput.OutputNotEscaped ?>
+				</div>
+			</div>
+			<?php
 			return;
 		}