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/__tests__/lib/order/code-gen.test.ts

@@ -0,0 +1,21 @@
+import { describe, it, expect } from 'vitest';
+import { generateRechargeCode } from '@/lib/order/code-gen';
+
+describe('generateRechargeCode', () => {
+  it('should generate code with s2p_ prefix', () => {
+    const code = generateRechargeCode('cm1234567890');
+    expect(code).toBe('s2p_cm1234567890');
+  });
+
+  it('should truncate long order IDs to fit 32 chars', () => {
+    const longId = 'a'.repeat(50);
+    const code = generateRechargeCode(longId);
+    expect(code.length).toBeLessThanOrEqual(32);
+    expect(code.startsWith('s2p_')).toBe(true);
+  });
+
+  it('should handle empty string', () => {
+    const code = generateRechargeCode('');
+    expect(code).toBe('s2p_');
+  });
+});