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/states/skirmish_states/structures/base.rs

@@ -47,4 +47,8 @@ impl Structure for BaseBuilding {
     fn get_stress(&self) -> u8 {
         self.stress
     }
+
+    fn get_name(&self) -> &'static str {
+        "Base"
+    }
 }