Use b for building and r for recruitment

- Replace Ctrl+Space with `b` and Alt+Space with `r` in README and
  documentation.
- Remove the old Alt+Space recruitment keybinding and adjust key
  handling code.
- Revamp skirmish view to display colored lines and updated status
  messages.
- Increase test suite to 83 tests and update test expectations for new
  shortcuts.
- Update flake.lock with the latest revision and hash.

tests/construction.rs

@@ -145,7 +145,7 @@ fn construction_view_starts_paid_build_on_enter_and_stays_open() -> () {
     }
     handle_keybindings(
         &mut app,
-        KeyEvent::new(KeyCode::Char(' '), KeyModifiers::CONTROL),
+        KeyEvent::new(KeyCode::Char('b'), KeyModifiers::NONE),
     );
     assert!(
         available_skirmish_actions(&app.states_ref().unwrap().skirmish).contains(&Action::Enter)
@@ -361,7 +361,7 @@ fn panel_shows_progress_and_delete_cancels_while_escape_only_closes_panel() -> (
     }
     handle_keybindings(
         &mut app,
-        KeyEvent::new(KeyCode::Char(' '), KeyModifiers::CONTROL),
+        KeyEvent::new(KeyCode::Char('b'), KeyModifiers::NONE),
     );
     handle_keybindings(&mut app, KeyEvent::new(KeyCode::Enter, KeyModifiers::NONE));
     assert!(
@@ -395,7 +395,7 @@ fn panel_shows_progress_and_delete_cancels_while_escape_only_closes_panel() -> (
     ));
     handle_keybindings(
         &mut app,
-        KeyEvent::new(KeyCode::Char(' '), KeyModifiers::CONTROL),
+        KeyEvent::new(KeyCode::Char('b'), KeyModifiers::NONE),
     );
     handle_keybindings(&mut app, KeyEvent::new(KeyCode::Delete, KeyModifiers::NONE));
     assert!(matches!(