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/src/views/admin/DashboardPage.vue

@@ -0,0 +1,98 @@
+<script setup lang="ts">
+import { onMounted } from 'vue'
+import { toast } from 'vue-sonner'
+import { Card, CardContent, CardHeader, CardTitle } from '@/components/ui/card'
+import { Skeleton } from '@/components/ui/skeleton'
+import { Button } from '@/components/ui/button'
+import { useAccountsStore } from '@/stores/accounts'
+import { Users, CheckCircle, XCircle, Armchair, RefreshCw } from 'lucide-vue-next'
+
+const accountsStore = useAccountsStore()
+
+onMounted(() => {
+  loadData()
+})
+
+async function loadData() {
+  try {
+    await accountsStore.fetchAccounts()
+  } catch (e: any) {
+    toast.error(e.message || '加载数据失败')
+  }
+}
+</script>
+
+<template>
+  <div class="space-y-6">
+    <div class="flex items-center justify-between">
+      <h1 class="text-2xl font-bold">Dashboard</h1>
+      <Button variant="outline" size="sm" @click="loadData" :disabled="accountsStore.loading">
+        <RefreshCw :class="['h-4 w-4 mr-2', accountsStore.loading && 'animate-spin']" />
+        刷新
+      </Button>
+    </div>
+
+    <!-- Stats Cards -->
+    <div class="grid gap-4 md:grid-cols-2 lg:grid-cols-4">
+      <!-- Total Teams -->
+      <Card>
+        <CardHeader class="flex flex-row items-center justify-between space-y-0 pb-2">
+          <CardTitle class="text-sm font-medium">Team 总数</CardTitle>
+          <Users class="h-4 w-4 text-muted-foreground" />
+        </CardHeader>
+        <CardContent>
+          <Skeleton v-if="accountsStore.loading" class="h-8 w-16" />
+          <div v-else class="text-2xl font-bold">{{ accountsStore.totalTeams }}</div>
+        </CardContent>
+      </Card>
+
+      <!-- Valid Teams -->
+      <Card>
+        <CardHeader class="flex flex-row items-center justify-between space-y-0 pb-2">
+          <CardTitle class="text-sm font-medium">有效订阅</CardTitle>
+          <CheckCircle class="h-4 w-4 text-green-500" />
+        </CardHeader>
+        <CardContent>
+          <Skeleton v-if="accountsStore.loading" class="h-8 w-16" />
+          <div v-else class="text-2xl font-bold text-green-600">{{ accountsStore.validTeams }}</div>
+        </CardContent>
+      </Card>
+
+      <!-- Invalid Teams -->
+      <Card>
+        <CardHeader class="flex flex-row items-center justify-between space-y-0 pb-2">
+          <CardTitle class="text-sm font-medium">无效订阅</CardTitle>
+          <XCircle class="h-4 w-4 text-red-500" />
+        </CardHeader>
+        <CardContent>
+          <Skeleton v-if="accountsStore.loading" class="h-8 w-16" />
+          <div v-else class="text-2xl font-bold text-red-600">{{ accountsStore.invalidTeams }}</div>
+        </CardContent>
+      </Card>
+
+      <!-- Available Seats -->
+      <Card>
+        <CardHeader class="flex flex-row items-center justify-between space-y-0 pb-2">
+          <CardTitle class="text-sm font-medium">剩余席位</CardTitle>
+          <Armchair class="h-4 w-4 text-muted-foreground" />
+        </CardHeader>
+        <CardContent>
+          <Skeleton v-if="accountsStore.loading" class="h-8 w-16" />
+          <div v-else class="text-2xl font-bold">{{ accountsStore.totalAvailableSeats }}</div>
+        </CardContent>
+      </Card>
+    </div>
+
+    <!-- Error state -->
+    <Card v-if="accountsStore.error" class="border-destructive">
+      <CardContent class="pt-6">
+        <div class="flex items-center justify-between">
+          <p class="text-destructive">{{ accountsStore.error }}</p>
+          <Button variant="outline" size="sm" @click="loadData">
+            重试
+          </Button>
+        </div>
+      </CardContent>
+    </Card>
+  </div>
+</template>