Refactor GameMode and Players into skirmish_states

Move the GameMode and Players enums from the top‑level states module
into the
skirmish_states submodule, add an Unclaimed variant to Players, and
update all
imports, trait implementations, and related logic accordingly. Adjust
the
durability percentage calculation to use u32 for safety.

src/app/states/skirmish_states/mod.rs

@@ -1,11 +1,15 @@
 mod board;
 mod focused_cell;
+mod game_mode;
 mod offset;
+mod players;
 pub mod structures;
 pub mod units;
 pub mod zoom_level;
 
 pub use board::BoardState;
 pub use focused_cell::{FocusedCell, MoveFocusedCell};
+pub use game_mode::GameMode;
 pub use offset::Offset;
+pub use players::Players;
 pub use zoom_level::{CellSizes, ZoomLevel};