refactor(database): 优化租户相关SQL查询逻辑

- 移除嵌套子查询，改用子查询中取最小user_id方式关联管理员用户
- 简化管理员用户相关字段的查询逻辑，提升SQL可读性
- 直接关联sys_user表替代以前复杂多层嵌套结构
- 保持查询结果字段一致，避免影响现有功能使用

src/main/java/com/gxwebsoft/common/system/mapper/xml/TenantMapper.xml

@@ -8,11 +8,7 @@
                u.phone,u.username
         FROM sys_tenant a
         LEFT JOIN sys_company b ON a.tenant_id = b.tenant_id
-        LEFT JOIN sys_user u ON u.tenant_id = a.tenant_id AND u.is_admin = 1
+        LEFT JOIN sys_user u ON u.tenant_id = a.tenant_id AND u.is_admin = 1 AND u.deleted = 0
-            AND u.user_id = (
-                SELECT MIN(user_id) FROM sys_user
-                WHERE tenant_id = a.tenant_id AND is_admin = 1 AND deleted = 0
-            )
         <where>
             <if test="param.tenantId != null">
                 AND a.tenant_id = #{param.tenantId}