feat(user): 调整用户账号校验规则- 修改用户账号正则表达式，允许最短1个字符

- 更新用户账号长度限制为1-30个字符
- 保持原有数字、字母、下划线组成规则不变

jeelowcode-service/jeelowcode-service-system-biz/src/main/java/com/jeelowcode/service/system/controller/vo/user/user/UserSaveReqVO.java

@@ -20,8 +20,8 @@ public class UserSaveReqVO {
 
     @Schema(description = "用户账号", requiredMode = Schema.RequiredMode.REQUIRED, example = "jeelowcode")
     @NotBlank(message = "用户账号不能为空")
-    @Pattern(regexp = "^[a-zA-Z0-9_]{4,30}$", message = "用户账号由 数字、字母、下划线 组成")
-    @Size(min = 4, max = 30, message = "用户账号长度为 4-30 个字符")
+    @Pattern(regexp = "^[a-zA-Z0-9_]{1,30}$", message = "用户账号由 数字、字母、下划线 组成")
+    @Size(min = 1, max = 30, message = "用户账号长度为 1-30 个字符")
     private String username;
 
     @Schema(description = "用户昵称", requiredMode = Schema.RequiredMode.REQUIRED, example = "芋艿")