fix: 侧边栏高亮逻辑清理与边界情况修复

- 移除 loadTabState 中冗余的 updateSidebarHighlight 调用（switchToTab/closeTab 已覆盖）
- 无文件夹+无标签时自动隐藏侧边栏（之前会空显示）
- handleSave/handleSaveAs 后刷新侧边栏（文件路径变化时同步更新）

renderer/renderer.js

@@ -545,15 +545,22 @@
     const tab = getActiveTab();
     const activePath = tab ? tab.filePath : null;
 
-    // If no folder is open, just re-render independent files
+    // 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);
       return;
     }
 
-    // Re-render independent files section (files may have been added/removed)
+    // Folder is open: re-render independent files section (files may have been added/removed)
     const oldSection = sidebarTree.querySelector('.independent-files-section');
     const newSection = renderIndependentFiles();
     if (oldSection) oldSection.remove();
@@ -619,15 +626,6 @@
     // Update modified state
     setModified(tab.isModified);
 
-    // Update sidebar highlight and independent files
-    updateSidebarHighlight();
-    // If no folder is open but we have open files, ensure sidebar is visible
-    if (!currentRootPath && tabs.length > 0) {
-      sidebar.classList.remove('collapsed');
-    } else if (!currentRootPath && tabs.length === 0) {
-      sidebar.classList.add('collapsed');
-    }
-
     // Notify main process about active file
     if (typeof window.electronAPI !== 'undefined') {
       window.electronAPI.tabSwitched(tab.filePath);
@@ -782,6 +780,7 @@
         tab.isModified = false;
         renderTabBar();
         updateTitle();
+        updateSidebarHighlight();
         statusText.textContent = '已保存';
         setTimeout(() => updateTitle(), 2000);
       }
@@ -810,6 +809,7 @@
         tab.isModified = false;
         renderTabBar();
         updateTitle();
+        updateSidebarHighlight();
         statusText.textContent = '已保存';
         setTimeout(() => updateTitle(), 2000);
       }