Add sidebar toggle button to breadcrumb with open/close functionality

Move sidebar toggle from sidebar panel to breadcrumb navigation, positioned
left of the HOME icon. Uses distinct icons for open (sidebar-inset) and
closed (sidebar) states. Sidebar state persists via sessionStorage. Remove
old non-functional toggle buttons from layout and HTMLBlock plugin.

public/assets/js/app.js

@@ -1,10 +1,61 @@
 // Main application JavaScript
 // This file contains general application functionality
 
+/**
+ * Toggle sidebar visibility (open/close)
+ */
+function toggleSidebar() {
+    const sidebar = document.getElementById('site-sidebar');
+    const contentCol = sidebar ? sidebar.nextElementSibling || sidebar.parentElement.querySelector('.content-column') : null;
+    const icon = document.querySelector('.sidebar-toggle-btn i');
+
+    if (!sidebar) return;
+
+    sidebar.classList.toggle('sidebar-hidden');
+
+    // Adjust content column width and toggle icon
+    if (sidebar.classList.contains('sidebar-hidden')) {
+        if (contentCol) {
+            contentCol.classList.remove('col-lg-9', 'col-md-8');
+            contentCol.classList.add('col-12');
+        }
+        if (icon) {
+            icon.classList.remove('bi-layout-sidebar-inset');
+            icon.classList.add('bi-layout-sidebar');
+        }
+        sessionStorage.setItem('sidebarHidden', 'true');
+    } else {
+        if (contentCol) {
+            contentCol.classList.remove('col-12');
+            contentCol.classList.add('col-lg-9', 'col-md-8');
+        }
+        if (icon) {
+            icon.classList.remove('bi-layout-sidebar');
+            icon.classList.add('bi-layout-sidebar-inset');
+        }
+        sessionStorage.setItem('sidebarHidden', 'false');
+    }
+}
+
+/**
+ * Restore sidebar state from sessionStorage on page load
+ */
+function restoreSidebarState() {
+    if (sessionStorage.getItem('sidebarHidden') === 'true') {
+        const sidebar = document.getElementById('site-sidebar');
+        if (sidebar) {
+            toggleSidebar();
+        }
+    }
+}
+
 // Initialize application when DOM is ready
 document.addEventListener('DOMContentLoaded', function() {
     console.log('CodePress CMS initialized');
     
+    // Restore sidebar state
+    restoreSidebarState();
+    
     // Handle nested dropdowns for touch devices
     const dropdownSubmenus = document.querySelectorAll('.dropdown-submenu');