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_state.h

@@ -16,9 +16,12 @@ struct GameState {
     bool paused = false;
     bool hardMode = false;
 
+    uint16_t curseTicksRemaining = 0;
+
     std::deque<std::array<int, 3>> snake;
     std::vector<std::array<int, 2>> apples;
     std::vector<std::array<int, 2>> bad_apples;
+    std::vector<std::array<int, 2>> cursed_apples;
 };
 
 #endif