feat: implement the new "Stop N Go" game mode, including phase management, dynamic safe zones, player missions, and dedicated UI with visual effects.

scripts/managers/player_action_manager.gd

@@ -181,10 +181,8 @@ func clear_highlights():
 			# Check Layer 2 (Overlay Highlight)
 			var l2_pos = Vector3i(cell.x, 2, cell.y)
 			var l2_item = enhanced_gridmap.get_cell_item(l2_pos)
-			# Only clear if it looks like a highlight (e.g. ID 1) 
-			# or generally just clear layer 2 if we assume we own it for highlights? 
-			# Safest is to check against hover_id or typical highlight IDs.
-			if l2_item != -1:
+			# Only clear if it is a highlight and NOT a Safe Zone (ID 2)
+			if l2_item != -1 and l2_item != 2:
 				enhanced_gridmap.set_cell_item(l2_pos, -1)
 	
 	highlighted_cells.clear()