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/widgets/keybindings.rs

@@ -115,9 +115,13 @@ impl Widget for KeybindingsWidget {
             return;
         }
 
-        let block: Block<'_> = Block::default()
-            .borders(Borders::ALL)
-            .title(block_single_title_helper("Keybindings", Color::Magenta));
+        let block: Block<'_> =
+            Block::default()
+                .borders(Borders::ALL)
+                .title(block_single_title_helper(
+                    "Keybindings".to_string(),
+                    Color::Magenta,
+                ));
 
         let inner: Rect = block.inner(area);