menu: guard against duplicate (add data-action to native button)

plugin.js

@@ -394,8 +394,10 @@
     var menuSubscribed = false;
     var menuInterval = null;
     function addMenuButton() {
-        // Use Lampa's native menu API (adds to .menu__list:eq(0) and wires hover:enter).
-        Lampa.Menu.addButton(
+        // Guard: only one copy (addButton does not set data-action, so we add it ourselves).
+        if ($('[data-action="' + PLUGIN.menu_action + '"]').length) return;
+        // Use Lampa's native menu API (adds to .menu__list and wires hover:enter).
+        var el = Lampa.Menu.addButton(
             '<svg class="sprite-folder"><use xlink:href="#sprite-folder"></use></svg>',
             t(PLUGIN.title),
             function () {
@@ -407,6 +409,7 @@
                 });
             }
         );
+        if (el && el.attr) el.attr('data-action', PLUGIN.menu_action);
     }
     function start() {
         if (menuSubscribed) return;