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

prisma/schema.prisma

@@ -16,7 +16,7 @@ model Order {
   status        OrderStatus @default(PENDING)
   paymentType   String      @map("payment_type")
 
-  zpayTradeNo   String?     @map("zpay_trade_no")
+  paymentTradeNo String?    @map("payment_trade_no")
   payUrl        String?     @map("pay_url")
   qrCode        String?     @map("qr_code")
   qrCodeImg     String?     @map("qr_code_img")