Fix sidebar collapse functionality

- Restored .sidebar.collapsed CSS class that was accidentally removed
- Sidebar toggle now works correctly with fixed header/footer layout

public/templates/layout.html

@@ -54,6 +54,10 @@
             height: 100%;
         }
         
+        .sidebar.collapsed {
+            margin-left: -250px;
+        }
+        
         .main-content {
             flex: 1;
             overflow-y: auto;