Vivre Sound ABX challenge

Open index.html in a browser and work through the ABX rows. For each trial,
decide whether X matches A or B, then record that answer in participant_abx.csv
or submit it at vivresound.com/abx.

This is an honesty test. Please do not inspect file hashes, sizes, timestamps,
or generated filenames while listening. The public package is blinded; the
server shows the answers only after a full submission.

Protocol notes:
- The media files are level-matched.
- Filenames are hashed.
- Catch trials are included.
- Aggregate results will be published when n is large enough.
