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/cli.rs

@@ -37,7 +37,7 @@ pub struct Cli {
         long,
         help = "Map width",
         value_name = "Positive integer [20; 100]",
-        default_value = "27"
+        default_value = "50"
     )]
     pub map_width: u8,
 
@@ -45,7 +45,7 @@ pub struct Cli {
         long,
         help = "Map height",
         value_name = "Positive integer [11; 50]",
-        default_value = "11"
+        default_value = "25"
     )]
     pub map_height: u8,