feat: migrate payment provider to easy-pay, add order history and refund support

- Replace zpay with easy-pay payment provider (new lib/easy-pay/ module)
- Add order history page for users (pay/orders)
- Add GET /api/orders/my endpoint to list user's own orders
- Add GET /api/users/[id] endpoint for sub2api user lookup
- Add order status tracking module (lib/order/status.ts)
- Update config to support easy-pay credentials (merchant ID, key, gateway)
- Update PaymentForm and PaymentQRCode components for easy-pay flow
- Update pay page and admin page with new order management UI
- Update order service to support easy-pay, cancellation, and refund

src/lib/db.ts

@@ -0,0 +1,14 @@
+import { PrismaClient } from '@prisma/client';
+import { PrismaPg } from '@prisma/adapter-pg';
+
+const globalForPrisma = globalThis as unknown as { prisma: PrismaClient };
+
+function createPrismaClient() {
+  const connectionString = process.env.DATABASE_URL ?? 'postgresql://localhost:5432/sub2apipay';
+  const adapter = new PrismaPg({ connectionString });
+  return new PrismaClient({ adapter });
+}
+
+export const prisma = globalForPrisma.prisma || createPrismaClient();
+
+if (process.env.NODE_ENV !== 'production') globalForPrisma.prisma = prisma;