docs: fix duplicate content and typo in spec

- Fix duplicate IndexedDB.databases method call typo
- Remove duplicate Popup lifecycle notes section

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

docs/superpowers/specs/2026-03-20-storage-cleaner-design.md

@@ -157,12 +157,12 @@ return count;
 #### 清理 IndexedDB
 
 ```javascript
-// 检查 databases indexedDB 方法是否可用
+// 检查 indexedDB.databases 方法是否可用
 if (typeof indexedDB.databases === 'function') {
   const databases = await indexedDB.databases();
   let count = 0;
   for (const db of databases) {
-    const deleteReq = indexedDB.databases(db.name);
+    const deleteReq = indexedDB.deleteDatabase(db.name);
     deleteReq.onblocked = () => {
       console.warn('IndexedDB delete blocked:', db.name);
     };
@@ -251,12 +251,6 @@ await chrome.tabs.reload(tab.id);
 - 刷新页面后 Popup 会自动关闭
 - 需要在刷新前显示提示："页面即将刷新，Popup 将关闭"
 
-**Popup 生命周期说明：**
-
-- Popup 在页面失去焦点时会关闭
-- 刷新页面后 Popup 会自动关闭
-- 需要在刷新前显示提示："页面即将刷新，Popup 将关闭"
-
 ## 权限需求
 
 需要在 manifest 中添加 `cookies` 权限：