refactor(tenant): 优化租户管理员用户查询逻辑

- 修改TenantMapper中sys_user的关联查询方式
- 使用ROW_NUMBER窗口函数获取每个租户的第一个管理员用户
- 过滤出is_admin为1且未删除的用户，提高查询准确性
- 避免直接按照user_id关联带来的潜在数据错误
- 保持查询结果结构不变，确保兼容现有业务逻辑

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

@@ -7,7 +7,16 @@
         SELECT a.*,b.company_name,b.company_logo as logo,b.admin_url,b.domain,b.free_domain,c.phone,c.username
         FROM sys_tenant a
         LEFT JOIN sys_company b ON a.tenant_id = b.tenant_id
-        LEFT JOIN sys_user c ON a.user_id = c.user_id
+        LEFT JOIN (
+            SELECT tenant_id, phone, username
+            FROM (
+                SELECT tenant_id, phone, username,
+                       ROW_NUMBER() OVER(PARTITION BY tenant_id ORDER BY user_id) AS rn
+                FROM sys_user
+                WHERE is_admin = 1 AND deleted = 0
+            ) t
+            WHERE rn = 1
+        ) c ON a.tenant_id = c.tenant_id
         <where>
             <if test="param.tenantId != null">
                 AND a.tenant_id = #{param.tenantId}