fix: 修复代码评审发现的 5 个问题

- P1 存量库回填：新增 0002 迁移，pricing/featured 从种子标签幂等回填，
  升级已有数据库不再出现定价筛选与首页精选无数据
- P1 Newsletter 双向同步：抽取 syncResendContact 助手并显式检查 SDK
  返回值中的 error 字段（Resend API 错误不抛异常）；退订接口同步
  Resend Audience 退订状态，重新订阅恢复订阅状态；订阅（active 分支）
  与退订链接均可重复触发同步，作为同步失败后的重试路径
- P1 后台表单：新增/编辑工具支持设置定价（含清空）与首页精选；
  顺带修掉 status 选项用 t("status")==="状态" 判断语言的 hack
- P2 分类缓存失效：分类增删改同时失效首页、工具列表与 ISR 分类落地页
- P2 收藏竞态：服务端改为 insert-first 原子 toggle，客户端加单工具
  pending 锁并以服务端返回状态收敛乐观更新

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

messages/en.json

@@ -319,7 +319,15 @@
         "updated": "Tool updated",
         "created": "Tool created",
         "updateFailed": "Update failed",
-        "createFailed": "Create failed"
+        "createFailed": "Create failed",
+        "statusDraft": "Draft",
+        "statusPublished": "Published",
+        "pricing": "Pricing",
+        "pricingNone": "Not set",
+        "pricingFree": "Free",
+        "pricingFreemium": "Freemium",
+        "pricingPaid": "Paid",
+        "featured": "Featured on homepage"
       }
     },
     "categoriesManagement": {

messages/zh.json

@@ -319,7 +319,15 @@
         "updated": "工具已更新",
         "created": "工具已创建",
         "updateFailed": "更新失败",
-        "createFailed": "创建失败"
+        "createFailed": "创建失败",
+        "statusDraft": "草稿",
+        "statusPublished": "已发布",
+        "pricing": "定价",
+        "pricingNone": "未设置",
+        "pricingFree": "免费",
+        "pricingFreemium": "免费增值",
+        "pricingPaid": "付费",
+        "featured": "首页精选"
       }
     },
     "categoriesManagement": {