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/states/settings.rs

@@ -4,8 +4,6 @@ use crate::app::states::{GameMode, PerkDecks};
 pub struct SettingsState {
     pub username: String,
     pub game_mode: GameMode,
-    pub map_width: u8,
-    pub map_height: u8,
     pub perk_deck: PerkDecks,
     pub starting_wood: u16,
     pub starting_iron: u16,