Adds default_bus_layout.tres at the addon root containing a Music bus and an
FX bus, each routing into Master. Users can point Project Settings → Audio →
Default Bus Layout at this file (or copy it to their project root) to get the
buses the players auto-route to in the editor. README documents the wiring.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
Daniel Samson