Open the co-op campaign in the editor

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/editor/mod.rs

@@ -534,6 +534,13 @@ impl Editor {
             self.open_dialog = false;
             return None;
         }
+        y += CH() * 2.2;
+        // the built-in co-op campaign, as a copy to change or to learn from
+        if im.button(gfx, Rect::new(x, y, bw * 2.0 + CW(), CH() * 1.7), &tr("net.coop_league")) {
+            self.load(coop_campaign::coop_campaign(), None);
+            self.open_dialog = false;
+            return None;
+        }
         y += CH() * 2.6;
         // a mission of the built-in campaign as a copy
         label(gfx, x, y, &tr("ed.template"), FRAME_HI);