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/state.rs

@@ -32,7 +32,9 @@ impl GameStates {
                     args.map_width as usize,
                     args.map_height as usize,
                     args.zoom_level,
+                    false,
                 ),
+                side_panel: false,
             },
             perk_decks: PerkDecksState {
                 id: 2,