Add side panel and refactor title helpers

Introduce a `side_panel` flag throughout the skirmish state, board
creation,
and cell area calculation to enable a detachable side panel. Refactor
the
title helper to own its strings and use a static separator, updating the
single‑title helper accordingly. Add a new `SidePanelWidget` and expose
the
`skirmish_main_area_layout` helper. Extend keybindings with `Tab` and
`ShiftTab` actions under a new `Opener` group. Update structures and
units
to implement a `get_name` method and adjust related traits and imports.

src/app/app.rs

@@ -60,7 +60,10 @@ impl App {
                     let Some(state) = self.states_mut() else {
                         panic!("State issue")
                     };
-                    state.skirmish.board.change_resize(&window_area);
+                    state
+                        .skirmish
+                        .board
+                        .change_resize(&window_area, state.skirmish.side_panel);
                 }
             }
         }