fix(client): 修复测试 timer 泄漏与编译 warning

- login_screen: Future.delayed 改为 Timer，dispose 时主动取消，
  避免测试框架报 pending timer 错误
- stock_in_form_screen: 移除未使用的 repository import，
  items 去掉无效 ?? [] 死代码（items 字段非空）
- stock_out_form_screen: 同上

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

client/lib/screens/stock_in/stock_in_form_screen.dart

@@ -8,7 +8,6 @@ import '../../providers/partner_provider.dart';
 import '../../providers/product_provider.dart';
 import '../../providers/stock_in_provider.dart';
 import '../../providers/warehouse_provider.dart';
-import '../../repositories/stock_in_repository.dart';
 
 class StockInFormScreen extends ConsumerStatefulWidget {
   final int? editOrderId;
@@ -55,7 +54,7 @@ class _StockInFormScreenState extends ConsumerState<StockInFormScreen> {
         }
         _remarkCtrl.text = order.remark ?? '';
         _items.clear();
-        for (final item in order.items ?? []) {
+        for (final item in order.items) {
           final row = _ItemRow();
           row.productId = item.productId;
           row.qtyCtrl.text = item.quantity.toStringAsFixed(0);