Support archive (tarball/zip) submissions for model competitions (#34) - Read submission files as bytes (Vec<u8>) instead of String to handle binary archives without crashing on invalid UTF-8 - Change submit_solution signature from &str to &[u8] for file content - Add is_archive_file() helper to detect .tar.gz, .tgz, .zip files - Skip popcorn directive parsing for archive files (return empty directives)