CellWidget::set_selected and set_marked now return &mut Self for method
chaining. Added BoardState::undo_marked_cell to remove the last marked
cell and restore focus. Backspace triggers undo, Delete clears marking.
Introduce a MoveFocusedCell enum and a BoardState.change_focused_cell
method to
centralize focus movement logic. Update skirmish keybindings to use this
new
method and simplify board rendering by directly using stored CellWidget
state.
Make CellWidget setters chainable and expose the new enum in the module
re‑exports. Remove duplicated max_offset logic and old move_* methods.
Extract Offset and FocusedCell structs from skirmish.rs into a new
skirmish_states module. Re-export the structs from the top-level states
module and adjust imports in skirmish.rs.
GarandPLG