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/components/admin/PaymentMethodChart.tsx

@@ -0,0 +1,61 @@
+'use client';
+
+interface PaymentMethod {
+  paymentType: string;
+  amount: number;
+  count: number;
+  percentage: number;
+}
+
+interface PaymentMethodChartProps {
+  data: PaymentMethod[];
+  dark?: boolean;
+}
+
+const TYPE_CONFIG: Record<string, { label: string; light: string; dark: string }> = {
+  alipay: { label: '支付宝', light: 'bg-blue-500', dark: 'bg-blue-400' },
+  wechat: { label: '微信支付', light: 'bg-green-500', dark: 'bg-green-400' },
+  stripe: { label: 'Stripe', light: 'bg-purple-500', dark: 'bg-purple-400' },
+};
+
+export default function PaymentMethodChart({ data, dark }: PaymentMethodChartProps) {
+  if (data.length === 0) {
+    return (
+      <div className={['rounded-xl border p-6', dark ? 'border-slate-700 bg-slate-800/60' : 'border-slate-200 bg-white shadow-sm'].join(' ')}>
+        <h3 className={['mb-4 text-sm font-semibold', dark ? 'text-slate-200' : 'text-slate-800'].join(' ')}>支付方式分布</h3>
+        <p className={['text-center text-sm py-8', dark ? 'text-slate-500' : 'text-gray-400'].join(' ')}>暂无数据</p>
+      </div>
+    );
+  }
+
+  return (
+    <div className={['rounded-xl border p-6', dark ? 'border-slate-700 bg-slate-800/60' : 'border-slate-200 bg-white shadow-sm'].join(' ')}>
+      <h3 className={['mb-4 text-sm font-semibold', dark ? 'text-slate-200' : 'text-slate-800'].join(' ')}>支付方式分布</h3>
+      <div className="space-y-4">
+        {data.map((method) => {
+          const config = TYPE_CONFIG[method.paymentType] || {
+            label: method.paymentType,
+            light: 'bg-gray-500',
+            dark: 'bg-gray-400',
+          };
+          return (
+            <div key={method.paymentType}>
+              <div className="mb-1.5 flex items-center justify-between text-sm">
+                <span className={dark ? 'text-slate-300' : 'text-slate-700'}>{config.label}</span>
+                <span className={dark ? 'text-slate-400' : 'text-slate-500'}>
+                  ¥{method.amount.toLocaleString()} · {method.percentage}%
+                </span>
+              </div>
+              <div className={['h-3 w-full overflow-hidden rounded-full', dark ? 'bg-slate-700' : 'bg-slate-100'].join(' ')}>
+                <div
+                  className={['h-full rounded-full transition-all', dark ? config.dark : config.light].join(' ')}
+                  style={{ width: `${method.percentage}%` }}
+                />
+              </div>
+            </div>
+          );
+        })}
+      </div>
+    </div>
+  );
+}