basic gameplay for cooperative

src/ui/BottomMenu.h

@@ -15,12 +15,13 @@ namespace ui {
 
 enum class BottomMenuItem : int {
     Play = 0,
-    Challenge = 1,
-    Level = 2,
-    Options = 3,
-    Help = 4,
-    About = 5,
-    Exit = 6,
+    Cooperate = 1,
+    Challenge = 2,
+    Level = 3,
+    Options = 4,
+    Help = 5,
+    About = 6,
+    Exit = 7,
 };
 
 struct Button {
@@ -37,8 +38,8 @@ struct BottomMenu {
 BottomMenu buildBottomMenu(const MenuLayoutParams& params, int startLevel);
 
 // Draws the cockpit HUD menu (PLAY + 4 bottom items) using existing UIRenderer primitives.
-// hoveredIndex: -1..5
-// selectedIndex: 0..5 (keyboard selection)
+// hoveredIndex: -1..7
+// selectedIndex: 0..7 (keyboard selection)
 // alphaMul: 0..1 (overall group alpha)
 void renderBottomMenu(SDL_Renderer* renderer,
                       FontAtlas* font,