fix: refresh-expiration 添加默认值 7 天，避免配置缺失时启动失败

zhijiayun-user/src/main/java/com/xuekairui/user/util/JwtUtil.java

@@ -31,8 +31,8 @@ public class JwtUtil {
     @Value("${jwt.admin-expiration:43200000}")
     private Long adminExpiration;      // 默认 12 小时
 
-    @Value("${jwt.refresh-expiration:}")
-    private Long refreshExpiration;
+    @Value("${jwt.refresh-expiration:604800000}")
+    private Long refreshExpiration;    // 默认 7 天
 
     private static final String ROLE_ADMIN = "ADMIN";
     private static final String ROLE_SUPER_ADMIN = "SUPER_ADMIN";