Background music (GUI)

Background music plays only in the Swing GUI. It is data-driven and external:

Put .ogg (OGG Vorbis) files in a music/ folder next to where you run the game. This folder is git-ignored and never bundled in the JAR.
A room plays a track via an optional music: field in rooms.yaml, e.g. music: manor-theme.ogg. Entering a room with a different track fades the old one out and the new one in (sequential, not an overlapping cross-fade); a room with no music: field fades to silence; the same track keeps playing seamlessly across rooms.
Volume is the Music setting (Off / Low / Medium / High) in the Settings menu, persisted to saves/settings.json. Off disables playback.
Missing files are ignored (silent) — the game never crashes over absent audio.
The console version is always silent.

Decoding uses the vorbisspi + jorbis libraries via the javax.sound SPI.