refactor(client): 只读判断统一走 WriteGuard 控件

将各屏内联的 ref.watch(isReadonlyProvider) 只读判断统一改为
WriteGuard(child:) 或 WriteGuard.isReadonly(ref)，全项目只读逻辑
单一入口（仅 write_guard.dart 内部保留 provider 读取）。行为不变。

121 测试通过，analyze 无 error。

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

client/lib/screens/inventory/inventory_list_screen.dart

@@ -9,6 +9,7 @@ import '../../core/responsive/responsive.dart';
 import '../../core/theme/app_theme.dart';
 import '../../models/inventory.dart';
 import '../../core/auth/auth_state.dart';
+import '../../widgets/write_guard.dart';
 import '../../providers/inventory_provider.dart';
 import '../../widgets/data_table_card.dart';
 import '../../widgets/mobile_list_card.dart';
@@ -292,7 +293,7 @@ class _InventoryListScreenState extends ConsumerState<InventoryListScreen> {
           message: item.remark.isEmpty ? '' : item.remark,
           waitDuration: const Duration(milliseconds: 300),
           child: GestureDetector(
-            onTap: ref.watch(isReadonlyProvider)
+            onTap: WriteGuard.isReadonly(ref)
                 ? null
                 : () => _editRemark(context, item),
             child: Row(
@@ -360,7 +361,7 @@ class _InventoryListScreenState extends ConsumerState<InventoryListScreen> {
           MobileCardField('供应商', item.supplierName),
       ],
       actions: [
-        if (!ref.watch(isReadonlyProvider))
+        if (!WriteGuard.isReadonly(ref))
           TextButton(
             onPressed: () => _editRemark(context, item),
             child: const Text('备注', style: TextStyle(fontSize: 13)),
@@ -554,7 +555,7 @@ class _InventoryListScreenState extends ConsumerState<InventoryListScreen> {
                     ref.read(inventoryListProvider.notifier).setPageSize(s),
                 toolbar: Row(
                   children: [
-                    if (!ref.watch(isReadonlyProvider)) ...[
+                    if (!WriteGuard.isReadonly(ref)) ...[
                       OutlinedButton.icon(
                         onPressed: () => context.go('/inventory/check'),
                         icon: const Icon(Icons.fact_check, size: 16),