fix: 收藏夹弹窗优化 — 已收藏标识 + 移除确认 + 点击可靠性

- 收藏夹选项中已收藏项显示黄色'已收藏'徽章，一目了然
- 点击判断改用 classList.contains('active') 替代 JS 变量，防 currentFolderId 为空
- addToFolder 兜底处理'已在此收藏夹中'错误，不弹 alert
- 取消收藏确认文案优化为'确定移出该收藏夹吗？'

templates/shared/static/js/utils.js

@@ -127,7 +127,7 @@ function showConfirm(title, message) {
         var overlay = document.createElement('div');
         setStyles(overlay, {
             position: 'fixed', inset: '0', background: 'rgba(0,0,0,0.4)',
-            zIndex: '9998', display: 'flex', alignItems: 'center', justifyContent: 'center'
+            zIndex: '10000', display: 'flex', alignItems: 'center', justifyContent: 'center'
         });
 
         // 弹窗容器
@@ -209,7 +209,7 @@ function showPrompt(message, defaultValue) {
         var overlay = document.createElement('div');
         setStyles(overlay, {
             position: 'fixed', inset: '0', background: 'rgba(0,0,0,0.4)',
-            zIndex: '9998', display: 'flex', alignItems: 'center', justifyContent: 'center'
+            zIndex: '10000', display: 'flex', alignItems: 'center', justifyContent: 'center'
         });
 
         // 弹窗容器