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/states/skirmish_states/board.rs

@@ -51,7 +51,7 @@ impl BoardState {
         let h_max_offset: usize = Self::max_offset(map_width, cols);
 
         let vertical_offset: Offset = Offset::new(
-            Some((map_height - rows as usize + 1) / 2),
+            Some(map_height.saturating_sub(rows).div_ceil(2)),
             Some(v_max_offset),
         );
         let horizontal_offset: Offset = Offset::new(None, Some(h_max_offset));