Add zoom support and emoji keybinding icons

- CellWidget now stores a ZoomLevel, renders size‑dependent text, and
  provides
  methods to set the zoom level and build its block.
- BoardState creates cells with the current zoom level, adds a helper to
  get a
  mutable cell, and updates each cell’s zoom level in `zoom_change`.
- KeybindingsWidget constructor now takes the widget height, calculates
  vertical padding to centre groups, and adds left borders between
  groups.
- Views (default, main_menu, skirmish) pass the area height to the new
  constructor.
- Keybinding descriptions are replaced with emoji symbols (🔈, 🔊, 🔉).
- BoardWidget clones the cell template instead of dereferencing it.

src/app/states/skirmish_states/board.rs

@@ -45,7 +45,7 @@ impl BoardState {
 
         for row in 0..map_height {
             for col in 0..map_width {
-                cells.push(CellWidget::new(row, col));
+                cells.push(CellWidget::new(row, col, zoom_level));
             }
         }
 
@@ -65,6 +65,10 @@ impl BoardState {
         }
     }
 
+    fn get_mut_cell(&mut self, row: usize, col: usize) -> &mut CellWidget {
+        &mut self.cells[row * self.map_width + col]
+    }
+
     pub fn zoom_change(&mut self, new_zoom_level: ZoomLevel) {
         self.zoom_level = new_zoom_level;
 
@@ -88,6 +92,12 @@ impl BoardState {
             self.map_height,
             self.map_width,
         );
+
+        for row in 0..self.map_height {
+            for col in 0..self.map_width {
+                self.get_mut_cell(row, col).set_zoom_level(new_zoom_level);
+            }
+        }
     }
 
     fn max_offset(map_size: usize, size: usize) -> usize {