Add scrolling actions and board widget

Introduce directional and scroll actions, update keybindings, add
scrollbar
state to SkirmishState, and render the board with a new BoardWidget.
Adjust CLI
defaults and layout heights accordingly.

src/app/widgets/board.rs

@@ -0,0 +1,75 @@
+use crate::app::{App, widgets::CellWidget};
+use ratatui::{
+    buffer::Buffer,
+    layout::{Constraint, Layout, Rect},
+    widgets::Widget,
+};
+use std::rc::Rc;
+
+pub struct BoardWidget {
+    cell_width: u16,
+    cell_height: u16,
+    cols: u16,
+    rows: u16,
+    h_offset: usize,
+    v_offset: usize,
+}
+
+impl BoardWidget {
+    pub fn new(app: &App, area_width: u16, area_height: u16) -> Self {
+        let cell_width: u16 = 7;
+        let cell_height: u16 = 4;
+
+        let cols: u16 = area_width / cell_width;
+        let rows: u16 = area_height / cell_height;
+
+        let h_max_offset: u16 = if app.states.settings.map_height as u16 > rows {
+            app.states.settings.map_height as u16 - rows
+        } else {
+            0
+        };
+
+        let v_max_offset: u16 = if app.states.settings.map_width as u16 > cols {
+            app.states.settings.map_width as u16 - cols
+        } else {
+            0
+        };
+
+        // let h_offset: usize = (cell_height * rows as u16 / area_height) as usize;
+        // let v_offset: usize = (cell_width * cols as u16 / area_width) as usize;
+
+        Self {
+            cell_width,
+            cell_height,
+            cols,
+            rows,
+            h_offset: h_max_offset as usize,
+            v_offset: v_max_offset as usize,
+        }
+    }
+}
+
+impl Widget for BoardWidget {
+    fn render(self, area: Rect, buf: &mut Buffer) {
+        let horizontal: Rc<[Rect]> = Layout::horizontal(vec![
+            Constraint::Length(self.cell_width);
+            self.cols as usize
+        ])
+        .split(area);
+
+        for (col_idx, col_area) in horizontal.iter().enumerate() {
+            let vertical: Rc<[Rect]> = Layout::vertical(vec![
+                Constraint::Length(self.cell_height);
+                self.rows as usize
+            ])
+            .split(*col_area);
+
+            for (row_idx, cell_area) in vertical.iter().enumerate() {
+                let cell: CellWidget =
+                    CellWidget::new(row_idx + self.v_offset, col_idx + self.h_offset);
+
+                cell.render(*cell_area, buf);
+            }
+        }
+    }
+}