fix: 侧边栏始终可见，不因无文件而隐藏

侧边栏包含「打开文件夹」入口，隐藏会导致用户无法打开文件夹

renderer/renderer.js

@@ -547,13 +547,6 @@
 
     // No folder open: manage independent files section
     if (!currentRootPath) {
-      if (tabs.length === 0) {
-        // No tabs and no folder — hide sidebar
-        sidebar.classList.add('collapsed');
-        sidebarTree.innerHTML = '';
-        return;
-      }
-      sidebar.classList.remove('collapsed');
       sidebarTree.innerHTML = '';
       const indepSection = renderIndependentFiles();
       if (indepSection) sidebarTree.appendChild(indepSection);