feat: 营养用餐侧边栏新增「自由餐品库」菜单项

在「餐品总库」与「算法标准」之间新增自由餐品库入口，页面内容暂复制自餐品总库，后续将做差异化。同步更新全部 26 个营养用餐分组页面侧边栏及 SITE_MAP。

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

index.html

@@ -294,6 +294,7 @@ const SITE_MAP = [
       { file:'sup-clean-external.html', label:'净菜外售' },
       { file:'din-user-mgmt.html', label:'用户管理' },
       { file:'din-dish-all.html', label:'菜品总库' },
+      { file:'din-dish-free.html', label:'自由餐品库' },
       { file:'din-dish-all-dialog.html', label:'菜品总库弹窗', dialog:true },
       { file:'din-dish-add.html', label:'新增菜品' },
       { file:'din-ingredient.html', label:'食材管理' },