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.

assets/css/frontend/homepage-fixed/base-1.css

@@ -112,14 +112,10 @@
   }
 }
 
+/* Dual-column geometry is owned by body.site-layout-* float rules in layout.css. */
 .aksrt-homepage__content-layout {
-  gap: 20px;
-}
-
-@media (min-width: 992px) {
-  .aksrt-homepage__content-layout {
-    grid-template-columns: minmax(0, 1fr) var(--sidebar-width, 311px);
-  }
+  display: block;
+  gap: 0;
 }
 
 @media (max-width: 1200px) {