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/side_panel.rs

@@ -0,0 +1,74 @@
+use ratatui::{
+    buffer::Buffer,
+    layout::{Alignment, Rect},
+    style::Color,
+    text::Line,
+    widgets::{Block, BorderType, Borders, Paragraph, Widget},
+};
+
+use crate::app::helpers::block_title_helper;
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct SidePanelWidget {
+    coords: (usize, usize),
+    structure_name: &'static str,
+    unit_name: &'static str,
+}
+
+impl SidePanelWidget {
+    pub fn new(
+        coords: (usize, usize),
+        structure_name: &'static str,
+        unit_name: &'static str,
+    ) -> Self {
+        Self {
+            coords,
+            structure_name,
+            unit_name,
+        }
+    }
+
+    fn col_to_letters(&self) -> String {
+        let mut col: usize = self.coords.1 + 1;
+        let mut letters: Vec<char> = Vec::new();
+
+        while col > 0 {
+            letters.push((b'A' + ((col - 1) % 26) as u8) as char);
+            col = (col - 1) / 26;
+        }
+
+        letters.iter().rev().collect()
+    }
+
+    fn get_title(&self) -> Line<'_> {
+        let cell_coords: String = format!("{}{}", self.col_to_letters(), self.coords.0);
+
+        let mut texts: Vec<(String, Color)> = Vec::with_capacity(3);
+
+        texts.push((cell_coords, Color::Yellow));
+        texts.push((self.structure_name.to_string(), Color::Cyan));
+
+        if !self.unit_name.is_empty() {
+            texts.push((self.unit_name.to_string(), Color::Green));
+        }
+
+        block_title_helper(&texts, Some(" - "))
+    }
+
+    fn get_block(&self) -> Block<'_> {
+        Block::default()
+            .borders(Borders::ALL)
+            .border_type(BorderType::Double)
+            .title(self.get_title())
+            .title_alignment(Alignment::Center)
+    }
+}
+
+impl Widget for SidePanelWidget {
+    fn render(self, area: Rect, buf: &mut Buffer) {
+        Paragraph::default()
+            .alignment(Alignment::Center)
+            .block(self.get_block())
+            .render(area, buf);
+    }
+}