feat: LDAP 账号管理 — OU管理/添加用户/删除用户/批量导入

后端新增 4 个 LDAP 管理端点:
- POST /ldap-config/create-ou: 创建组织单元
- POST /ldap-config/create-user: 创建单个用户 (SSHA加密)
- POST /ldap-config/delete-user: 删除用户
- POST /ldap-config/batch-import-ldap: 批量导入用户
- POST /ldap-config/user-list: 查询用户列表(恢复)

前端 LdapConfigPage 增强:
- LDAP 账号管理折叠区(配置存在即显示)
- OU 下拉选择 + 根节点选项 + 数量统计
- 用户列表表格(全选/单选/DN显示)
- 新建 OU 弹框(名称+父级DN+描述)
- 添加用户弹框(用户名+密码+显示名+邮箱+目标OU)
- 删除选中用户按钮(确认后批量删除)

前端 UsersPage BatchImportModal 三 Tab:
- 本地导入 / 导入到 LDAP / 从 LDAP 导入

测试修复:
- test_user_endpoint.py: 分页格式兼容
- test_users.py: 分页格式兼容
- test_system_settings.py: 精简后配置项匹配

backend/tests/test_user.py

@@ -25,8 +25,9 @@ class TestListUsers:
         resp = await client.get("/api/v1/users", headers=auth_header(admin_token))
         assert resp.status_code == 200
         data = resp.json()
-        assert isinstance(data, list)
-        assert len(data) >= 1
+        items = data.get("items", data) if isinstance(data, dict) else data
+        assert isinstance(items, list)
+        assert len(items) >= 1
 
     async def test_list_users_role_filter(self, client: AsyncClient, admin_user, admin_token):
         """按 role 筛选用户。"""
@@ -35,7 +36,9 @@ class TestListUsers:
             headers=auth_header(admin_token),
         )
         assert resp.status_code == 200
-        for u in resp.json():
+        data = resp.json()
+        items = data.get("items", data) if isinstance(data, dict) else data
+        for u in items:
             assert u["role"] == "admin"
 
     async def test_list_users_is_active_filter(
@@ -47,7 +50,9 @@ class TestListUsers:
             headers=auth_header(admin_token),
         )
         assert resp.status_code == 200
-        for u in resp.json():
+        data = resp.json()
+        items = data.get("items", data) if isinstance(data, dict) else data
+        for u in items:
             assert u["is_active"] is False
 
     async def test_list_users_combined_filters(
@@ -59,7 +64,9 @@ class TestListUsers:
             headers=auth_header(admin_token),
         )
         assert resp.status_code == 200
-        for u in resp.json():
+        data = resp.json()
+        items = data.get("items", data) if isinstance(data, dict) else data
+        for u in items:
             assert u["role"] == "developer"
             assert u["is_active"] is False
 
@@ -70,7 +77,9 @@ class TestListUsers:
             headers=auth_header(admin_token),
         )
         assert resp.status_code == 200
-        assert resp.json() == []
+        data = resp.json()
+        items = data.get("items", data) if isinstance(data, dict) else data
+        assert items == []
 
     async def test_list_users_non_admin_forbidden(
         self, client: AsyncClient, developer_token