Initialize skirmish board and refactor states

- Create `GameStates` from a `&Cli` and initialize the skirmish board in
  `App::new`.
- Move map dimensions to `SkirmishState` and add a `board_cells` vector
  populated by `CellWidget`s.
- Refactor `SettingsState` to store only user‑specific settings (fields
  are cloned).
- Update `BoardWidget` to hold a reference to the cell vector and use
  the new dimensions.
- Adjust CLI defaults: map width to 50 and map height to 25.

src/app/widgets/cell.rs

@@ -13,6 +13,7 @@ use ratatui::{
 //     Base,
 // }
 
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
 pub struct CellWidget {
     pub row: usize,
     pub col: usize,