feat: 管理后台数据看板

新增 /admin/dashboard 页面，提供充值订单统计与分析：
- 汇总统计卡片（今日/累计充值金额、订单数、成功率、平均充值）
- 每日充值趋势折线图（recharts，支持 7/30/90 天切换）
- 充值排行榜（Top 10 用户）
- 支付方式分布（水平条形图）
- 与 /admin 订单管理页面互相导航

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/app/admin/dashboard/page.tsx

@@ -0,0 +1,155 @@
+'use client';
+
+import { useSearchParams } from 'next/navigation';
+import { useState, useEffect, useCallback, Suspense } from 'react';
+import PayPageLayout from '@/components/PayPageLayout';
+import DashboardStats from '@/components/admin/DashboardStats';
+import DailyChart from '@/components/admin/DailyChart';
+import Leaderboard from '@/components/admin/Leaderboard';
+import PaymentMethodChart from '@/components/admin/PaymentMethodChart';
+
+interface DashboardData {
+  summary: {
+    today: { amount: number; orderCount: number; paidCount: number };
+    total: { amount: number; orderCount: number; paidCount: number };
+    successRate: number;
+    avgAmount: number;
+  };
+  dailySeries: { date: string; amount: number; count: number }[];
+  leaderboard: { userId: number; userName: string | null; userEmail: string | null; totalAmount: number; orderCount: number }[];
+  paymentMethods: { paymentType: string; amount: number; count: number; percentage: number }[];
+  meta: { days: number; generatedAt: string };
+}
+
+const DAYS_OPTIONS = [7, 30, 90] as const;
+
+function DashboardContent() {
+  const searchParams = useSearchParams();
+  const token = searchParams.get('token');
+  const theme = searchParams.get('theme') === 'dark' ? 'dark' : 'light';
+  const uiMode = searchParams.get('ui_mode') || 'standalone';
+  const isDark = theme === 'dark';
+  const isEmbedded = uiMode === 'embedded';
+
+  const [days, setDays] = useState<number>(30);
+  const [data, setData] = useState<DashboardData | null>(null);
+  const [loading, setLoading] = useState(true);
+  const [error, setError] = useState('');
+
+  const fetchData = useCallback(async () => {
+    if (!token) return;
+    setLoading(true);
+    setError('');
+    try {
+      const res = await fetch(`/api/admin/dashboard?token=${encodeURIComponent(token)}&days=${days}`);
+      if (!res.ok) {
+        if (res.status === 401) {
+          setError('管理员凭证无效');
+          return;
+        }
+        throw new Error('请求失败');
+      }
+      setData(await res.json());
+    } catch {
+      setError('加载数据失败');
+    } finally {
+      setLoading(false);
+    }
+  }, [token, days]);
+
+  useEffect(() => {
+    fetchData();
+  }, [fetchData]);
+
+  if (!token) {
+    return (
+      <div className={`flex min-h-screen items-center justify-center p-4 ${isDark ? 'bg-slate-950' : 'bg-slate-50'}`}>
+        <div className="text-center text-red-500">
+          <p className="text-lg font-medium">缺少管理员凭证</p>
+          <p className="mt-2 text-sm text-gray-500">请从 Sub2API 平台正确访问管理页面</p>
+        </div>
+      </div>
+    );
+  }
+
+  const navParams = new URLSearchParams();
+  navParams.set('token', token);
+  if (theme === 'dark') navParams.set('theme', 'dark');
+  if (isEmbedded) navParams.set('ui_mode', 'embedded');
+
+  const btnBase = [
+    'inline-flex items-center rounded-lg border px-3 py-1.5 text-xs font-medium transition-colors',
+    isDark ? 'border-slate-600 text-slate-200 hover:bg-slate-800' : 'border-slate-300 text-slate-700 hover:bg-slate-100',
+  ].join(' ');
+
+  const btnActive = [
+    'inline-flex items-center rounded-lg px-3 py-1.5 text-xs font-medium',
+    isDark ? 'bg-indigo-500/30 text-indigo-200 ring-1 ring-indigo-400/40' : 'bg-blue-600 text-white',
+  ].join(' ');
+
+  return (
+    <PayPageLayout
+      isDark={isDark}
+      isEmbedded={isEmbedded}
+      maxWidth="full"
+      title="数据概览"
+      subtitle="充值订单统计与分析"
+      actions={
+        <>
+          {DAYS_OPTIONS.map((d) => (
+            <button
+              key={d}
+              type="button"
+              onClick={() => setDays(d)}
+              className={days === d ? btnActive : btnBase}
+            >
+              {d}天
+            </button>
+          ))}
+          <a href={`/admin?${navParams}`} className={btnBase}>
+            订单管理
+          </a>
+          <button type="button" onClick={fetchData} className={btnBase}>
+            刷新
+          </button>
+        </>
+      }
+    >
+      {error && (
+        <div className={`mb-4 rounded-lg border p-3 text-sm ${isDark ? 'border-red-800 bg-red-950/50 text-red-400' : 'border-red-200 bg-red-50 text-red-600'}`}>
+          {error}
+          <button onClick={() => setError('')} className="ml-2 opacity-60 hover:opacity-100">
+            ✕
+          </button>
+        </div>
+      )}
+
+      {loading ? (
+        <div className={`py-24 text-center ${isDark ? 'text-slate-400' : 'text-gray-500'}`}>加载中...</div>
+      ) : data ? (
+        <div className="space-y-6">
+          <DashboardStats summary={data.summary} dark={isDark} />
+          <DailyChart data={data.dailySeries} dark={isDark} />
+          <div className="grid gap-6 lg:grid-cols-2">
+            <Leaderboard data={data.leaderboard} dark={isDark} />
+            <PaymentMethodChart data={data.paymentMethods} dark={isDark} />
+          </div>
+        </div>
+      ) : null}
+    </PayPageLayout>
+  );
+}
+
+export default function DashboardPage() {
+  return (
+    <Suspense
+      fallback={
+        <div className="flex min-h-screen items-center justify-center">
+          <div className="text-gray-500">加载中...</div>
+        </div>
+      }
+    >
+      <DashboardContent />
+    </Suspense>
+  );
+}