Runs mvn clean package (and optionally -P modern) and identifies the correct output JAR paths under bukkit/target/, bungeecord/target/, and velocity/target/. Use when user says 'build', 'package', 'release', 'create JAR', or 'deploy'. Reminds about shade relocations and the jar.suffix property. Do NOT use for dependency updates, adding new modules, or platform-specific code changes.