fix(frontend): stop single sidebar float overlap under fixed nav

Replace the fragile content-wrap float + negative-margin sidebar with a
main.container grid, add fixed-nav top breathing room so the breadcrumb
stays below the header, and mark the aside as content-layout__aside.

inc/helpers/aksrt-single.php

@@ -948,7 +948,7 @@ if (!function_exists('aksrt_single_render_aside')) :
 			return;
 		}
 		?>
-		<div class="sidebar" role="complementary" aria-label="<?php esc_attr_e('侧栏', 'aksrt'); ?>">
+		<aside class="sidebar content-layout__aside" role="complementary" aria-label="<?php esc_attr_e('侧栏', 'aksrt'); ?>">
 			<?php if (!empty($ctx['has_download'])) : ?>
 				<?php get_template_part('templates/parts/resource-meta-box'); ?>
 			<?php endif; ?>
@@ -971,7 +971,7 @@ if (!function_exists('aksrt_single_render_aside')) :
 			<?php if (is_active_sidebar('all_sidebar_bottom')) : ?>
 				<?php dynamic_sidebar('all_sidebar_bottom'); ?>
 			<?php endif; ?>
-		</div>
+		</aside>
 		<?php
 	}
 endif;