Add selectable soundtracks via CLI

Introduce a `Soundtrack` enum with Clap `ValueEnum` support and expose
it in the CLI as a `--sound-track` option. Extend `AudioCmd` with a
`ChangeSoundtrack` variant and refactor audio handling to load and cache
soundtracks per‑track using a thread‑safe `RwLock`. Update the
`handle_audio` function signature to accept the selected soundtrack,
adjust re‑exports, and modify `main` to pass the chosen soundtrack to
the audio thread. Also reposition the logging flag in the CLI
definition.

src/app/threads/mod.rs

@@ -2,6 +2,6 @@ pub mod audio;
 pub mod events;
 pub mod handle_events;
 
-pub use audio::{AudioCmd, SoundrackParts, handle_audio};
+pub use audio::{AudioCmd, SoundrackParts, Soundtrack, handle_audio};
 pub use events::AppEvent;
 pub use handle_events::handle_events;