feat(frontend): adopt zibll site-layout-1/2/3 float dual-column system

Wire settings-driven sidebar visibility and body site-layout classes,
replace content-layout CSS grid with Zibll float geometry, move sidebar
DOM to content-wrap sibling across single/archive/page/home, and add
post meta show_layout overrides.

single.php

@@ -27,7 +27,7 @@ while (have_posts()) :
 	}
 
 	$settings = is_array($ctx['settings'] ?? null) ? $ctx['settings'] : [];
-	$show_aside = !empty($ctx['show_aside']) && !wp_is_mobile();
+	$show_aside = !empty($ctx['show_aside']); // body site-layout-* is authoritative
 
 	get_header();
 	?>