接单工单支持置顶，抢单大厅优先展示

- 新增 work_orders.pinned_at 字段与迁移
- 管理端对已发布（待抢单）订单提供置顶/取消置顶操作，置顶订单带标记
- 抢单大厅按置顶时间优先排序，打手端卡片展示置顶标签

apps/frontend/src/services/admin/worker-platform.ts

@@ -283,6 +283,13 @@ export function unpublishAdminWorkOrder(workOrderId: number) {
   )
 }
 
+export function pinAdminWorkOrder(workOrderId: number, pinned: boolean) {
+  return apiPost<{ order: WorkOrder }>(
+    `/api/v1/admin/worker-platform/orders/${workOrderId}/pin`,
+    { pinned },
+  )
+}
+
 export function fetchAdminWorkOrderSharing(workOrderId: number) {
   return apiGet<{ order: WorkOrder; shares: WorkOrderShare[] }>(
     `/api/v1/admin/worker-platform/orders/${workOrderId}/sharing`,