chore(license): 添加文件头版权信息

- 为 MdSanitizer.java 文件添加了完整的版权和许可信息
- 添加了 GNU Affero General Public License 声明
- 包含了原项目 Symphony 的致谢信息
- 添加了修改版本的说明和版权归属

Author: csfwff

src/main/java/org/b3log/symphony/util/MdSanitizer.java

@@ -1,3 +1,21 @@
+/*
+ * Rhythm - A modern community (forum/BBS/SNS/blog) platform written in Java.
+ * Modified version from Symphony, Thanks Symphony :)
+ * Copyright (C) 2012-present, b3log.org
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
 package org.b3log.symphony.util;
 
 import java.util.regex.Pattern;