feat: 优化数据操作体验，使用乐观更新

- 保存/删除操作立即更新UI，无需等待API
- 避免页面闪烁和数据重新加载
- API失败时自动恢复数据

frontend/src/App.jsx

@@ -125,12 +125,16 @@ function App() {
       }
       if (editingCategory) {
         await categoryApi.update(editingCategory.id, payload)
+        // 乐观更新：直接修改列表中的项
+        setCategories(categories.map(c => c.id === editingCategory.id ? { ...c, ...payload } : c))
       } else {
-        await categoryApi.create(payload)
+        const res = await categoryApi.create(payload)
+        // 乐观更新：添加到列表
+        const newCat = res.data
+        setCategories([...categories, newCat])
       }
       setCategoryForm({ name: '', icon: 'folder', color: '#667eea', sort_order: 0 })
       setEditingCategory(null)
-      loadData()
     } catch (e) { console.error(e) } finally {
       setSaving(false)
     }
@@ -138,11 +142,18 @@ function App() {
 
   const deleteCategory = async (id) => {
     if (!confirm('确定删除该分类？该分类下的网站将变为未分类状态。')) return
+    // 乐观删除：先从UI移除
+    const catName = categories.find(c => c.id === id)?.name
+    setCategories(categories.filter(c => c.id !== id))
+    // 网站也更新为未分类
+    setWebsites(websites.map(s => s.category_id === id ? { ...s, category_id: null, category: null } : s))
+    if (selectedCategory === id) setSelectedCategory(null)
     try {
       await categoryApi.delete(id)
-      if (selectedCategory === id) setSelectedCategory(null)
+    } catch (e) {
+      // 失败则恢复
       loadData()
-    } catch (e) {}
+    }
   }
 
   // 保存网站
@@ -151,13 +162,17 @@ function App() {
     setSaving(true)
     try {
       const payload = { ...websiteForm, category_id: websiteForm.category_id || null }
+      const catName = categories.find(c => c.id === websiteForm.category_id)?.name
       if (modal.data) {
         await websiteApi.update(modal.data.id, payload)
+        // 乐观更新
+        setWebsites(websites.map(s => s.id === modal.data.id ? { ...s, ...payload, category: catName ? { name: catName } : null } : s))
       } else {
-        await websiteApi.create(payload)
+        const res = await websiteApi.create(payload)
+        const newSite = { ...res.data, category: catName ? { name: catName } : null }
+        setWebsites([...websites, newSite])
       }
       closeModal()
-      loadData()
     } catch (e) {} finally {
       setSaving(false)
     }
@@ -165,10 +180,13 @@ function App() {
 
   const handleDeleteWebsite = async (id) => {
     if (!confirm('确定删除？')) return
+    // 乐观删除
+    setWebsites(websites.filter(s => s.id !== id))
     try {
       await websiteApi.delete(id)
+    } catch (e) {
       loadData()
-    } catch (e) {}
+    }
   }
 
   const toggleFavorite = async (site) => {