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

@@ -4,19 +4,15 @@
 
     <!-- 关联查询sql -->
     <sql id="selectSql">
-        SELECT a.*,b.company_name,b.company_logo as logo,b.admin_url,b.domain,b.free_domain,c.phone,c.username
+        SELECT a.*,b.company_name,b.company_logo as logo,b.admin_url,b.domain,b.free_domain,
+               u.phone,u.username
         FROM sys_tenant a
         LEFT JOIN sys_company b ON a.tenant_id = b.tenant_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
+        LEFT JOIN sys_user u ON u.tenant_id = a.tenant_id AND u.is_admin = 1
+            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}