Refactor buildings/units, move CellTag & Players

Introduce BaseBuilding struct. Rename Building and Unit to enum types
(Buildings, Units). Move CellTag and Players enums to the skirmish state
module and update imports and re‑exports accordingly. Add placeholder
miner module.

src/app/states/mod.rs

@@ -9,5 +9,5 @@ pub use main_menu::MainMenuState;
 pub use perk_decks::{PerkDecks, PerkDecksState};
 pub use settings::SettingsState;
 pub use skills_config::SkillsConfigState;
-pub use skirmish::{GameMode, SkirmishState, ZoomLevel};
+pub use skirmish::{CellTag, GameMode, Players, SkirmishState, ZoomLevel};
 pub use skirmish_states::{FocusedCell, Offset};

src/app/states/skirmish.rs

@@ -20,3 +20,16 @@ pub enum ZoomLevel {
     Default,
     ZoomedOut,
 }
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum CellTag {
+    Base(Players),
+    Tunel,
+    Stone,
+}
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum Players {
+    Player,
+    Enemy,
+}

src/app/states/skirmish_states/board.rs

@@ -1,7 +1,7 @@
 use crate::app::{
     helpers::{CellSizes, cell_size_helper, cells_area_helper},
-    states::{FocusedCell, Offset, ZoomLevel, skirmish_states::MoveFocusedCell},
-    widgets::{CellTag, CellWidget, Players},
+    states::{CellTag, FocusedCell, Offset, Players, ZoomLevel, skirmish_states::MoveFocusedCell},
+    widgets::CellWidget,
 };
 use ratatui::layout::Rect;