style(SidebarMenu): 优化菜单项淡入淡出效果

- 为菜单项文本和操作添加过渡效果，实现平滑淡入淡出
- 修改菜单项折叠时的样式，使用透明度和宽度变化来实现淡出效果

biji-qianduan/src/components/home/SidebarMenu.vue

@@ -222,12 +222,16 @@ const renderMenu = (item) => {
   overflow: hidden;
   text-overflow: ellipsis;
   flex-grow: 1;
+  transition: opacity 0.2s ease; /* Add transition for smooth fade */
+  opacity: 1;
 }
 
 .menu-item-actions {
   display: none;
   align-items: center;
   gap: 5px;
+  transition: opacity 0.2s ease;
+  opacity: 1;
 }
 
 .el-menu:not(.el-menu--collapse) .el-menu-item:hover .menu-item-actions,
@@ -237,7 +241,8 @@ const renderMenu = (item) => {
 
 .el-menu--collapse .menu-item-text,
 .el-menu--collapse .menu-item-actions {
-  display: none;
+  opacity: 0; /* Fade out instead of just disappearing */
+  width: 0; /* Ensure it takes no space */
 }
 
 .edit-icon, .delete-icon {