fix(sidebar): collapse empty sidebar column on every scene

Sidebar visibility had two disconnected decisions: the body site-layout-*
class (via aksrt_is_show_sidebar_filter) only checked widget activity for
singles, while the homepage aside renderer skipped the column and
sidebar.php rendered an empty one. With the toggle on and no widgets, the
homepage kept a reserved gutter and squeezed the main content aside.

- collapse every scene to no-sidebar when the sidebar widget stack is empty
- resolve home_sidebar before the page branch so a static front page is
  checked against the zones the homepage renders
- guard the homepage aside with aksrt_is_show_sidebar() alone and drop the
  duplicate aksrt_homepage_has_sidebar gate
- early-return sidebar.php instead of rendering an empty column
- drop dead code: archive helper $preferred param, wp_is_mobile fallback,
  container--no-sidebar class, unreachable front-page fallback
- update post-visual-contract to pin the single visibility decision

Verification: php -l on all changed files; node --test
tests/widget-system/*.test.cjs 242/243 (the toast-contract failure is
pre-existing and unrelated).

inc/helpers/homepage/content.php

@@ -139,35 +139,15 @@ if (!function_exists('aksrt_homepage_render_widget_zone')) {
 	}
 }
 
-if (!function_exists('aksrt_homepage_has_sidebar')) {
-	/**
-	 * Whether the fixed homepage should render an aside column.
-	 */
-	function aksrt_homepage_has_sidebar(): bool {
-		$has_widgets = function_exists('aksrt_has_current_sidebar_widgets')
-			? aksrt_has_current_sidebar_widgets()
-			: aksrt_homepage_has_active_sidebars([
-				'all_sidebar_top',
-				'home_sidebar',
-				'all_sidebar_bottom',
-			]);
-		if (!$has_widgets) {
-			return false;
-		}
-
-		if (function_exists('aksrt_is_show_sidebar')) {
-			return aksrt_is_show_sidebar();
-		}
-		return true;
-	}
-}
-
 if (!function_exists('aksrt_homepage_render_sidebar')) {
 	/**
 	 * Render the homepage aside column.
+	 *
+	 * Visibility is aksrt_is_show_sidebar() alone; its filter already
+	 * collapses the layout when the sidebar widget stack is empty.
 	 */
 	function aksrt_homepage_render_sidebar(): void {
-		if (!aksrt_homepage_has_sidebar()) {
+		if (!aksrt_is_show_sidebar()) {
 			return;
 		}