refactor(system): 优化用户导出功能

- 移除 UserMapper 中的性别转换逻辑
- 在 UserServiceImpl 中添加字典数据获取和性别转换逻辑

src/main/resources/mapper/system/UserMapper.xml

@@ -184,11 +184,7 @@
             u.nickname,
             u.mobile,
             u.email,
-            CASE u.gender
-                WHEN 1 THEN '男'
-                WHEN 2 THEN '女'
-                ELSE '保密'
-            END gender,
+            u.gender,
             d.NAME AS dept_name,
             u.create_time
         FROM