Replace one unverified audio cue with a redistributable sound

[aribradshaw]

Goal

Replace one WAV file listed as unresolved in docs/ASSET_RIGHTS.md with a clearly redistributable sound.

Suggested scope

Start with one short interface cue. Record or source a replacement under CC0 or another repository-compatible license, keep the file small, and preserve the existing sound helper API.

Acceptance criteria

• The replacement has a stable source URL, author, and license record.
• docs/ASSET_RIGHTS.md is updated for that exact file.
• The old sample is removed from source control.
• Gameplay and browser tests remain green.