feat(tenant): 新增用户租户关联关系API

- 在SysTenantController中新增addUserTenant接口用于处理用户租户关联
- 完善SysTenantServiceImpl中用户岗位关联逻辑的空值检查
- 新增用户租户关联DTO参数校验和权限控制

pigx-upms/pigx-upms-biz/src/main/java/com/pig4cloud/pigx/admin/controller/SysTenantController.java

@@ -200,6 +200,12 @@ public class SysTenantController {
         return R.ok(sysTenantService.getUserTenant());
     }
 
+    /**
+     * 新增用户租户关联关系
+     *
+     * @param tenantUserDTO 用户租户关联信息DTO
+     * @return 操作结果
+     */
     @PostMapping("/user-tenant")
     @HasPermission("sys_systenant_del")
     public R addUserTenant(@RequestBody SysTenantUserDTO tenantUserDTO) {

pigx-upms/pigx-upms-biz/src/main/java/com/pig4cloud/pigx/admin/service/impl/SysTenantServiceImpl.java

@@ -429,7 +429,7 @@ public class SysTenantServiceImpl extends ServiceImpl<SysTenantMapper, SysTenant
                         .eq(SysUserPost::getUserId, userId)
                         .eq(SysUserPost::getPostId, tenantUserDTO.getPostId()));
 
-                if (CollUtil.isEmpty(userPostList)) {
+                if (CollUtil.isEmpty(userPostList) && Objects.nonNull(tenantUserDTO.getPostId())) {
                     // 插入用户岗位关系
                     SysUserPost sysUserPost = new SysUserPost();
                     sysUserPost.setUserId(userId);