fix(client): 出入库录单 golden 随日期漂移——表单支持钉死单据日期

根因：表单 _orderDate 默认 DateTime.now()，golden 07-04 录制后每天必挂
（整屏 diff 只有日期格一个数字）。表单加 initialDate 测试注入口，
golden 测试钉死 2026-07-04，基准图零重录、永不随日期漂移。

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01JJ1g8XV1YhhmHRzhwWEW7o

client/lib/screens/stock_in/stock_in_form_screen.dart

@@ -27,7 +27,10 @@ import '../../widgets/ds/ds_toast.dart';
 /// 明细为可键盘操作的内联网格（名称/系列/规格可搜索+新增，生产日期/批次/数量/单价/售价内联编辑）。
 class StockInFormScreen extends ConsumerStatefulWidget {
   final int? editOrderId;
-  const StockInFormScreen({super.key, this.editOrderId});
+
+  /// 仅供 golden 测试钉死单据日期（默认 DateTime.now() 会让 golden 随日期漂移）。
+  final DateTime? initialDate;
+  const StockInFormScreen({super.key, this.editOrderId, this.initialDate});
 
   @override
   ConsumerState<StockInFormScreen> createState() => _StockInFormScreenState();
@@ -39,7 +42,7 @@ class _StockInFormScreenState extends ConsumerState<StockInFormScreen> {
   final _warehouseFocus = FocusNode();
   int? _warehouseId;
   int? _partnerId;
-  DateTime _orderDate = DateTime.now();
+  late DateTime _orderDate = widget.initialDate ?? DateTime.now();
   bool _submitting = false;
   bool _loadingEdit = false;
   StockInOrder? _loadedOrder;

client/lib/screens/stock_out/stock_out_form_screen.dart

@@ -142,7 +142,10 @@ class _ItemRow {
 /// 明细行经「从库存批量选择」添加，商品/系列/规格/可用只读，仅数量、售价可内联编辑。
 class StockOutFormScreen extends ConsumerStatefulWidget {
   final int? editOrderId;
-  const StockOutFormScreen({super.key, this.editOrderId});
+
+  /// 仅供 golden 测试钉死单据日期（默认 DateTime.now() 会让 golden 随日期漂移）。
+  final DateTime? initialDate;
+  const StockOutFormScreen({super.key, this.editOrderId, this.initialDate});
 
   @override
   ConsumerState<StockOutFormScreen> createState() => _StockOutFormScreenState();
@@ -154,7 +157,7 @@ class _StockOutFormScreenState extends ConsumerState<StockOutFormScreen> {
   final _warehouseFocus = FocusNode();
   int? _warehouseId;
   int? _partnerId;
-  DateTime _orderDate = DateTime.now();
+  late DateTime _orderDate = widget.initialDate ?? DateTime.now();
   bool _submitting = false;
   bool _loadingEdit = false;
   Map<int, double> _inventoryMap = {};

client/test/golden/stock_in_form_golden_test.dart

@@ -73,7 +73,7 @@ void main() {
   goldenAcrossThemes(
     'stock-in form 录单(桌面)',
     goldenPrefix: 'stock_in_form',
-    child: () => const Scaffold(body: StockInFormScreen()),
+    child: () => Scaffold(body: StockInFormScreen(initialDate: DateTime(2026, 7, 4))),
     overrides: _overrides,
     logical: const Size(1280, 920),
   );
@@ -81,7 +81,7 @@ void main() {
   goldenAcrossThemes(
     'stock-in form 录单(移动)',
     goldenPrefix: 'stock_in_form_mobile',
-    child: () => const Scaffold(body: StockInFormScreen()),
+    child: () => Scaffold(body: StockInFormScreen(initialDate: DateTime(2026, 7, 4))),
     overrides: _overrides,
     logical: const Size(390, 1400),
   );

client/test/golden/stock_out_form_golden_test.dart

@@ -53,7 +53,7 @@ void main() {
   goldenAcrossThemes(
     'stock-out form 录单(桌面)',
     goldenPrefix: 'stock_out_form',
-    child: () => const Scaffold(body: StockOutFormScreen()),
+    child: () => Scaffold(body: StockOutFormScreen(initialDate: DateTime(2026, 7, 4))),
     overrides: _overrides,
     logical: const Size(1280, 920),
   );
@@ -61,7 +61,7 @@ void main() {
   goldenAcrossThemes(
     'stock-out form 录单(移动)',
     goldenPrefix: 'stock_out_form_mobile',
-    child: () => const Scaffold(body: StockOutFormScreen()),
+    child: () => Scaffold(body: StockOutFormScreen(initialDate: DateTime(2026, 7, 4))),
     overrides: _overrides,
     logical: const Size(390, 1400),
   );