Add tab navigation for building and recruitment UI

- Add selection indices and option lists to SkirmishState.
- Implement `cycle_popup_option` and expose Left/Right actions in
  keybindings.
- Introduce `cancel_focused_tasks` in BoardState for Delete handling.
- CellWidget now displays recruitment progress on Base structures.
- Update README and documentation to describe new tabs and arrow
  navigation.
- Adjust test counts and add extensive task‑cancellation tests.

tests/construction.rs

@@ -354,7 +354,7 @@ fn cancellation_restores_original_ore_and_refunds_cost_exactly_once() -> () {
 }
 
 #[test]
-fn panel_shows_progress_and_delete_cancels_while_escape_only_closes_panel() -> () {
+fn panel_shows_progress_delete_cancels_and_escape_is_ignored() -> () {
     let mut app: App = app();
     for _ in 0..2 {
         handle_keybindings(&mut app, KeyEvent::new(KeyCode::Left, KeyModifiers::NONE));
@@ -389,6 +389,7 @@ fn panel_shows_progress_and_delete_cancels_while_escape_only_closes_panel() -> (
     assert!(text.contains("Construction: 0%"));
     assert!(text.contains("Delete - Cancel construction"));
     handle_keybindings(&mut app, KeyEvent::new(KeyCode::Esc, KeyModifiers::NONE));
+    assert!(app.states_ref().unwrap().skirmish.building_view);
     assert!(matches!(
         app.states_ref().unwrap().skirmish.board.cells[5][1].get_structure(),
         Structures::MineConstruction(_)
@@ -397,6 +398,11 @@ fn panel_shows_progress_and_delete_cancels_while_escape_only_closes_panel() -> (
         &mut app,
         KeyEvent::new(KeyCode::Char('b'), KeyModifiers::NONE),
     );
+    assert!(!app.states_ref().unwrap().skirmish.building_view);
+    handle_keybindings(
+        &mut app,
+        KeyEvent::new(KeyCode::Char('b'), KeyModifiers::NONE),
+    );
     handle_keybindings(&mut app, KeyEvent::new(KeyCode::Delete, KeyModifiers::NONE));
     assert!(matches!(
         app.states_ref().unwrap().skirmish.board.cells[5][1].get_structure(),