Add tests, fix offset logic, and bump dependencies

- Introduce a comprehensive test suite (cli, app, board, tasks, audio)
  and a
  new TESTING.md document describing test execution.
- Correct vertical offset calculation in `BoardState` to use saturating
  subtraction and ceiling division.
- Clamp initial `Offset` values to the provided maximum in
  `Offset::new`.
- Export `load_audio` from the audio thread module and switch to
  `LoopedDecoder` for proper OGG looping.
- Update several crate versions: clap, ratatui, log, rodio, and
  bitflags.

src/app/threads/mod.rs

@@ -2,6 +2,6 @@ mod audio;
 mod events;
 mod tick;
 
-pub use audio::{AudioCmd, SoundrackParts, Soundtrack, handle_audio};
+pub use audio::{AudioCmd, SoundrackParts, Soundtrack, handle_audio, load_audio};
 pub use events::handle_ct_events;
 pub use tick::{TICK_MS, handle_tick_event};