feat(auth): 添加 UserType 枚举常量，区分 ADMIN 和 MEMBER 用户类型

gym-manage-api/manage-common/src/main/java/cn/novalon/gym/manage/common/constants/UserType.java

@@ -0,0 +1,22 @@
+package cn.novalon.gym.manage.common.constants;
+
+/**
+ * 用户类型枚举
+ * 用于区分后台管理用户和前台会员用户
+ */
+public enum UserType {
+    ADMIN,
+    MEMBER;
+
+    public static UserType fromString(String value) {
+        if (value == null) {
+            throw new IllegalArgumentException("userType 不能为空");
+        }
+        for (UserType type : values()) {
+            if (type.name().equalsIgnoreCase(value)) {
+                return type;
+            }
+        }
+        throw new IllegalArgumentException("未知的用户类型: " + value);
+    }
+}