feat: 实现前端卡密管理界面

- 卡密列表展示与分页功能

- 单个/批量创建卡密

- 卡密删除与批量删除

- 卡密导出功能 (file-saver)

- 启用/禁用状态切换

- 状态判断 (有效/已使用/已失效)

- Toast 通知系统 (vue-sonner)

- 登录页面错误提示优化

- 后端登录错误消息中文化

frontend/components.json

@@ -0,0 +1,21 @@
+{
+  "$schema": "https://shadcn-vue.com/schema.json",
+  "style": "new-york",
+  "typescript": true,
+  "tailwind": {
+    "config": "",
+    "css": "src/style.css",
+    "baseColor": "neutral",
+    "cssVariables": true,
+    "prefix": ""
+  },
+  "iconLibrary": "lucide",
+  "aliases": {
+    "components": "@/components",
+    "utils": "@/lib/utils",
+    "ui": "@/components/ui",
+    "lib": "@/lib",
+    "composables": "@/composables"
+  },
+  "registries": {}
+}