fix(pay): 待支付浮窗无刷新同步

- modal-cache 失效时广播 aksrt:cache:invalidated
- 新增 GET /orders/wait-pay-float 返回浮窗片段
- wait-pay-float.js 监听 orders 标签失效并替换/移除浮窗、重启倒计时
- VIP/充值/下载待支付分支触发 orders 失效

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

assets/js/cms-download.js

@@ -678,6 +678,7 @@
 						window.open(data.payment_url, '_blank');
 					}
 					renderScanPay(data, returnFocusEl);
+					if (window.AksrtModalRuntime) window.AksrtModalRuntime.invalidate(['orders']);
 					if (data.order_number) pollOrderPaid(data.order_number, returnFocusEl);
 					return;
 				}