fix: 指派审核功能修复

- pending recipes 初始化 _showAssign 和 _assignTo 属性
- 修复 Vue 响应式问题导致下拉框和发送按钮无反应

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

frontend/src/views/RecipeManager.vue

@@ -1264,7 +1264,9 @@ function onTagPickerSave(tags) {
 
 watch(() => recipeStore.recipes, () => {
   if (auth.isAdmin) {
-    const pending = recipeStore.recipes.filter(r => r._owner_id && r._owner_id !== auth.user.id)
+    const pending = recipeStore.recipes
+      .filter(r => r._owner_id && r._owner_id !== auth.user.id)
+      .map(r => ({ ...r, _showAssign: false, _assignTo: '' }))
     pendingRecipes.value = pending
     pendingCount.value = pending.length
   }