🐛 fix(av1-transfer): remove hardcoded /bin/bash, use default sh

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

av1-transfer/main.py

@@ -136,7 +136,6 @@ def transcode_one_file(file_info, overall_bar, slot_bars, slot_queue, process_na
             proc = subprocess.Popen(
                 f"exec -a {shlex.quote(process_name)} ffmpeg {shell_args}",
                 shell=True,
-                executable="/bin/bash",
                 stdout=subprocess.PIPE,
                 stderr=subprocess.PIPE,
             )