docs: add tool note to Main.java header

Author: lzwjava

src/main/java/com/lzw/solutions/codeforces/p2189C2/Main.java

@@ -1,3 +1,4 @@
+// grok-4.1-thinking
 package com.lzw.solutions.codeforces.p2189C2;
 
 import java.io.*;