fix: mobile responsive admin panel

frontend/admin/index.html

@@ -55,9 +55,20 @@
         </div>
     </aside>
 
+    <!-- Sidebar overlay (mobile) -->
+    <div class="sidebar-overlay" id="sidebar-overlay"></div>
+
     <!-- Main -->
     <main class="main">
         <header class="topbar">
+            <button class="menu-toggle" id="menu-toggle" aria-label="Меню">
+                <svg width="24" height="24" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2"
+                    stroke-linecap="round" stroke-linejoin="round">
+                    <line x1="3" y1="6" x2="21" y2="6" />
+                    <line x1="3" y1="12" x2="21" y2="12" />
+                    <line x1="3" y1="18" x2="21" y2="18" />
+                </svg>
+            </button>
             <h1>Управление пользователями</h1>
         </header>