chore: 添加 Java/Maven 构建产物到 .gitignore

排除 target/、*.class、*.jar、*.war，避免编译产物被误提交
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.gitignore

@@ -35,3 +35,9 @@ pip-delete-this-directory.txt
 .idea/
 .vscode/
 .DS_Store
+
+# Java / Maven
+target/
+*.class
+*.jar
+*.war