build: upgrade to Java 21 and reorganize documentation
-rwxr-xr-x 189 .gitignore
-rw-r--r-- 10706 AGENTS.md
-rw-r--r-- 7048 COPYING
drwxr-xr-x - Documentation
-rw-r--r-- 3317 TODO.org
drwxr-xr-x - Tools
drwxr-xr-x - commandline launcher
-rw-r--r-- 5897 pom.xml
drwxr-xr-x - src
drwxr-xr-x - usage examples