Add base tags, adjust margins, update CLI defaults

Introduce `CellTag` and `Players` enums and extend `CellWidget` to carry
a tag.
Store player and enemy base coordinates in `BoardState` and tag those
cells.
Reduce horizontal margin from 3 to 1 in board layout helpers.
Change CLI defaults: map width default 42, map height min 11 and default
11.
Adjust offset calculation and render constraints to match the new
layout.

src/app/helpers/cells_area.rs

@@ -9,7 +9,7 @@ pub fn cells_area_helper(area: &Rect) -> Rect {
         .borders(Borders::LEFT | Borders::TOP | Borders::RIGHT)
         .inner(skirmish_layout(*area)[1])
         .inner(Margin {
-            horizontal: 3,
+            horizontal: 1,
             vertical: 1,
         })
 }