refactor: extract pay page components and migrate zpay → easypay

Components:
- Add PayPageLayout, OrderFilterBar, MobileOrderList, OrderTable, OrderSummaryCards
- Extract shared pay-utils (types, constants, helper functions)
- Simplify pay/page.tsx and orders/page.tsx

EasyPay migration:
- Remove src/lib/zpay/, api/zpay/notify, zpay test, zpay.md
- Simplify config.ts: single envSchema, no ZPAY_* fallback
- Rename DB field zpay_trade_no → payment_trade_no (migration added)
- Update OrderDetail label: ZPAY订单号 → 支付单号
- Update CLAUDE.md project structure

src/components/OrderSummaryCards.tsx

@@ -0,0 +1,37 @@
+interface Summary {
+  total: number;
+  pending: number;
+  completed: number;
+  failed: number;
+}
+
+interface OrderSummaryCardsProps {
+  isDark: boolean;
+  summary: Summary;
+}
+
+export default function OrderSummaryCards({ isDark, summary }: OrderSummaryCardsProps) {
+  const cardClass = ['rounded-xl border p-3', isDark ? 'border-slate-700 bg-slate-800/70' : 'border-slate-200 bg-slate-50'].join(' ');
+  const labelClass = ['text-xs', isDark ? 'text-slate-400' : 'text-slate-500'].join(' ');
+
+  return (
+    <div className="mb-4 grid grid-cols-2 gap-3 sm:grid-cols-4">
+      <div className={cardClass}>
+        <div className={labelClass}>总订单</div>
+        <div className="mt-1 text-xl font-semibold">{summary.total}</div>
+      </div>
+      <div className={cardClass}>
+        <div className={labelClass}>待支付</div>
+        <div className="mt-1 text-xl font-semibold">{summary.pending}</div>
+      </div>
+      <div className={cardClass}>
+        <div className={labelClass}>已完成</div>
+        <div className="mt-1 text-xl font-semibold">{summary.completed}</div>
+      </div>
+      <div className={cardClass}>
+        <div className={labelClass}>异常/关闭</div>
+        <div className="mt-1 text-xl font-semibold">{summary.failed}</div>
+      </div>
+    </div>
+  );
+}