feat: 优化验证码超时显示效果，超时后显示已过期请刷新

continew-admin-common/src/main/java/top/continew/admin/common/model/resp/CaptchaResp.java

@@ -48,4 +48,7 @@ public class CaptchaResp implements Serializable {
      */
     @Schema(description = "验证码图片（Base64编码，带图片格式：data:image/gif;base64）", example = "data:image/png;base64,iVBORw0KGgoAAAAN...")
     private String img;
+
+    @Schema(description = "过期时间戳", example = "1714376969409")
+    private Long expireTime;
 }