feat(client): 只读角色隐藏所有写按钮（WriteGuard 统一控件 + 顶栏只读标识）

- 新增 isReadonlyProvider（role == 'readonly'）+ WriteGuard 控件，统一隐藏写控件
- 入库/出库/库存/商品/基础数据/往来单位/财务/设置 各屏：只读时隐藏
  新增/编辑/删除/审核/提交/驳回/结清/盘点/导入/激活/用户管理 等写操作
- 顶栏显示「只读」标识，让只读用户明确当前权限
- 后端 middleware.ReadOnly() 仍兜底 403，UI 隐藏 + 后端拦截双保险

修正：此前误判为后端漏洞/部署 bug，实为前端写按钮未对只读隐藏。
后端经验证正确拦截只读写操作（线上 stock-in/product-options 均 403）。

121 测试通过，analyze 无 error。

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

client/lib/screens/stock_out/stock_out_list_screen.dart

@@ -20,6 +20,7 @@ import '../../providers/inventory_provider.dart';
 import '../../providers/tab_state_provider.dart';
 import '../../providers/product_provider.dart';
 import '../../providers/finance_provider.dart' show financeRepositoryProvider;
+import '../../core/auth/auth_state.dart';
 
 class StockOutListScreen extends ConsumerStatefulWidget {
   const StockOutListScreen({super.key});
@@ -286,7 +287,7 @@ class _StockOutListScreenState extends ConsumerState<StockOutListScreen> {
           ref.read(stockOutListProvider.notifier).setPageSize(s),
       toolbar: Row(
         children: [
-          if (showNewButton)
+          if (showNewButton && !ref.watch(isReadonlyProvider))
             ElevatedButton.icon(
               onPressed: () => context.go('/stock-out/new'),
               icon: const Icon(Icons.add, size: 16),
@@ -350,6 +351,7 @@ class _StockOutListScreenState extends ConsumerState<StockOutListScreen> {
 
   /// 操作按钮列表，表格与移动端卡片共用。
   List<Widget> _orderActions(BuildContext context, StockOutOrder o) {
+    final readonly = ref.watch(isReadonlyProvider);
     return [
       TextButton(
         onPressed: () => _showDetail(context, o.id),
@@ -366,13 +368,13 @@ class _StockOutListScreenState extends ConsumerState<StockOutListScreen> {
         child: const Text('打印',
             style: TextStyle(fontSize: 12, color: AppTheme.primary)),
       ),
-      if (o.status == 'approved')
+      if (!readonly && o.status == 'approved')
         TextButton(
           onPressed: () => _confirmSettle(context, o.id, 'stock_out'),
           child: const Text('结清',
               style: TextStyle(fontSize: 12, color: AppTheme.accent)),
         ),
-      if (o.status == 'draft') ...[
+      if (!readonly && o.status == 'draft') ...[
         TextButton(
           onPressed: () => context.go('/stock-out/edit/${o.id}'),
           child: const Text('修改',
@@ -389,7 +391,7 @@ class _StockOutListScreenState extends ConsumerState<StockOutListScreen> {
               style: TextStyle(fontSize: 12, color: AppTheme.primary)),
         ),
       ],
-      if (o.status == 'pending') ...[
+      if (!readonly && o.status == 'pending') ...[
         TextButton(
           key: Key('btn_approve_${o.id}'),
           onPressed: () => _confirmApprove(context, o),