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/units/mod.rs

@@ -4,4 +4,4 @@ mod units_trait;
 
 pub use miner::MinerUnit;
 pub use units_enum::Units;
-pub use units_trait::{OptionalUnit, Unit};
+pub use units_trait::Unit;