Add cursed apple: a status-effect apple that inverts controls

Eating a cursed apple inverts the snake's steering for
CURSE_DURATION_TICKS ticks, shown on the top screen while active. The
sprite is a recolored copy of the rotten-apple tile since all existing
sprite tiles are already in use.

include/game_render.h

@@ -15,6 +15,7 @@ struct RenderAssets {
     u16 *gfx_apple = nullptr;
     u16 *gfx_tail = nullptr;
     u16 *gfx_apple_rotten = nullptr;
+    u16 *gfx_apple_cursed = nullptr;
 };
 
 void draw_game(const GameState &state, const RenderAssets &assets);