feat(client): 实时授权状态与会话失效处理

- 心跳读取 /auth/ping 回带的授权概况，直接刷新横幅/状态栏/只读门禁，省去单独轮询 /license/info
- 账号被停用/删除（401 USER_DISABLED）即强制重新登录
- 令牌持久化经串行队列 + 会话代号守卫，杜绝续期写入与登出交叉把失效 token 写回
- 写操作门禁（write_guard）+ 授权文案（license_copy）按 grace/readonly/locked 分阶段降级

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

client/lib/screens/finance/finance_screen.dart

@@ -169,10 +169,12 @@ class _FinanceTabState extends ConsumerState<_FinanceTab> {
       ],
       actions: (canClose && !WriteGuard.isReadonly(ref))
           ? [
-              TextButton(
-                onPressed: () => _closeRecord(r),
-                child: const Text('结清',
-                    style: TextStyle(fontSize: 13, color: AppTheme.success)),
+              WriteGuard(
+                child: TextButton(
+                  onPressed: () => _closeRecord(r),
+                  child: const Text('结清',
+                      style: TextStyle(fontSize: 13, color: AppTheme.success)),
+                ),
               ),
             ]
           : null,
@@ -318,10 +320,12 @@ class _FinanceTabState extends ConsumerState<_FinanceTab> {
           if ((r.type == 'payable' || r.type == 'receivable') &&
               r.status == 'open' &&
               !WriteGuard.isReadonly(ref)) {
-            return DataCell(TextButton(
-              onPressed: () => _closeRecord(r),
-              child: const Text('结清',
-                  style: TextStyle(fontSize: 12, color: AppTheme.success)),
+            return DataCell(WriteGuard(
+              child: TextButton(
+                onPressed: () => _closeRecord(r),
+                child: const Text('结清',
+                    style: TextStyle(fontSize: 12, color: AppTheme.success)),
+              ),
             ));
           }
           return const DataCell(SizedBox());
@@ -419,10 +423,12 @@ class _FinanceTabState extends ConsumerState<_FinanceTab> {
             toolbar: Row(
               children: [
                 if (addLabel != null && !WriteGuard.isReadonly(ref))
-                  ElevatedButton.icon(
-                    onPressed: _showAddDialog,
-                    icon: const Icon(Icons.add, size: 16),
-                    label: Text(addLabel),
+                  WriteGuard(
+                    child: ElevatedButton.icon(
+                      onPressed: _showAddDialog,
+                      icon: const Icon(Icons.add, size: 16),
+                      label: Text(addLabel),
+                    ),
                   ),
                 if (addLabel != null && !WriteGuard.isReadonly(ref))
                   const SizedBox(width: 8),