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.

source/game_input.cpp

@@ -30,23 +30,25 @@ bool handle_input_frame(InputContext &ctx) {
     }
 
     if (!ctx.state->paused && !ctx.state->gameOver) {
+        const bool cursed = ctx.state->curseTicksRemaining > 0;
+
         if ((keys != 0U) && ((keys & KEY_UP) != 0U)) {
-            ctx.state->snakeDirection = 0;
+            ctx.state->snakeDirection = cursed ? 2 : 0;
             draw_game(*ctx.state, *ctx.renderAssets);
         }
 
         if ((keys != 0U) && ((keys & KEY_RIGHT) != 0U)) {
-            ctx.state->snakeDirection = 1;
+            ctx.state->snakeDirection = cursed ? 3 : 1;
             draw_game(*ctx.state, *ctx.renderAssets);
         }
 
         if ((keys != 0U) && ((keys & KEY_DOWN) != 0U)) {
-            ctx.state->snakeDirection = 2;
+            ctx.state->snakeDirection = cursed ? 0 : 2;
             draw_game(*ctx.state, *ctx.renderAssets);
         }
 
         if ((keys != 0U) && ((keys & KEY_LEFT) != 0U)) {
-            ctx.state->snakeDirection = 3;
+            ctx.state->snakeDirection = cursed ? 1 : 3;
             draw_game(*ctx.state, *ctx.renderAssets);
         }
     }